Letters
Parylene-Based Double-Layer Gate Dielectrics for Organic Field-Effect Transistors
Hyunjin Park - ,
Hyungju Ahn - ,
Jimin Kwon - ,
Seongju Kim - , and
Sungjune Jung *
We demonstrate high-performance and stable organic field-effect transistors (OFETs) using parylene-based double-layer gate dielectrics (DLGDs). DLGDs, consisting of parylene C as the upper layer and F as the lower layer, are designed to simultaneously provide good interface and bulk gate dielectric properties by exploiting the advantages of each gate dielectric. The structural effects of DLGDs are systematically investigated by evaluating the electrical characteristics and dielectric properties while varying the thickness ratio of each gate dielectric. The OFET with the optimized DLGD exhibits high performance and operational stability. This systematic approach will be useful for realizing practical electronic applications.
CoSe2-Decorated NbSe2 Nanosheets Fabricated via Cation Exchange for Li Storage
Jianli Zhang - ,
Chengfeng Du - ,
Jin Zhao - ,
Hao Ren - ,
Qinghua Liang - ,
Yun Zheng - ,
Srinivasan Madhavi - ,
Xin Wang - ,
Junwu Zhu *- , and
Qingyu Yan *
Though 2D transition metal dichalcogenides have attracted a lot of attention in energy-storage applications, the applications of NbSe2 for Li storage are still limited by the unsatisfactory theoretical capacity and uncontrollable synthetic approaches. Herein, a controllable oil-phase synthetic route for preparation of NbSe2 nanoflowers consisted of nanosheets with a thickness of ∼10 nm is presented. Significantly, a part of NbSe2 can be further replaced by orthorhombic CoSe2 nanoparticles via a post cation exchange process, and the predominantly 2D nanosheet-like morphology can be well-maintained, resulting in the formation of CoSe2-decorated NbSe2 (denoted as CDN) nanosheets. More interestingly, the CDN nanosheets exhibit excellent lithium-ion battery performance. For example, it achieves a highly reversible capacity of 280 mAh g–1 at 10 A g–1 and long cyclic stability with specific capacity of 364.7 mAh g–1 at 5 A g–1 after 1500 cycles, which are significantly higher than those of reported pure NbSe2.
Click Chemistry: A Versatile Method for Tuning the Composition of Mixed Organic Layers Obtained by Reduction of Diazonium Cations
Marius Cesbron - ,
Eric Levillain - ,
Tony Breton *- , and
Christelle Gautier *
Postfunctionalization of glassy carbon electrodes previously modified by reduction of 4-azidobenzenediazonium was exploited to conveniently synthesize controlled mixed organic layers. Huisgen 1,3-dipolar cycloaddition was used to anchor functional entities to azide platform. By this way, ((4-ethynylphenyl)carbamoyl)ferrocene (ϕ-Fc) was coimmobilized with a set of acetylene derivatives: 1-ethynyl-4-nitrobenzene (ϕ-NO2), 4-ethynylaniline (ϕ-NH2) or ethylnylbenzene (ϕ). The composition of the resulting organic layers was tuned by adjusting the acetylene derivatives ratio in the postfunctionalization binary solution. Electronic properties of the substituents beared by the aromatic rings were found to have a strong impact on the cycloaddition kinetics toward the confined azide moieties. From this study, rules to prepare finely tuned bifunctional organic layers can be anticipated.
Biological and Medical Applications of Materials and Interfaces
NIPAM-based Microgel Microenvironment Regulates the Therapeutic Function of Cardiac Stromal Cells
Xiaolin Cui - ,
Junnan Tang - ,
Yusak Hartanto - ,
Jiabin Zhang - ,
Jingxiu Bi - ,
Sheng Dai - ,
Shi Zhang Qiao - ,
Ke Cheng *- , and
Hu Zhang *
To tune the chemical, physical, and mechanical microenvironment for cardiac stromal cells to treat acute myocardial infarction (MI), we prepared a series of thermally responsive microgels with different surface charges (positive, negative, and neutral) and different degrees of hydrophilicity, as well as functional groups (carboxyl, hydroxyl, amino, and methyl). These microgels were used as injectable hydrogels to create an optimized microenvironment for cardiac stromal cells (CSCs). Our results indicated that a hydrophilic and negatively charged microenvironment created from poly(N-isopropylacrylamide-co-itaconic acid) was favorable for maintaining high viability of CSCs, promoting CSC proliferation and facilitating the formation of CSC spheroids. A large number of growth factors, such as vascular endothelial growth factor (VEGF), insulin-like growth factor I (IGF-1), and stromal-derived factor-1 (SDF-1) were released from the spheroids, promoting neonatal rat cardiomyocyte activation and survival. After injecting the poly(N-isopropylacrylamide-co-itaconic acid) microgel into mice, we examined their acute inflammation and T-cell immune reactions. The microgel itself did not elicit obvious immune response. We then injected the same microgel-encapsulated with CSCs into MI mice. The result revealed the treatment-promoted MI heart repair through angiogenesis and inhibition of apoptosis with an improved cell retention rate. This study will open a door for tailoring poly(N-isopropylacrylamide)-based microgel as a delivery vehicle for CSC therapy.
Cascade Cytosol Delivery of Dual-Sensitive Micelle-Tailored Vaccine for Enhancing Cancer Immunotherapy
Dandan Jiang - ,
Weiwei Mu - ,
Xiuping Pang - ,
Yongjun Liu *- ,
Na Zhang *- ,
Yunmei Song - , and
Sanjay Garg
Enhancing cytosol delivery of exogenous antigens in antigen presenting cells can improve cross-presentation and CD8+ T cell-mediated immune response. The antigen cytosol delivery speed, which has great importance on the rate of MHC class I molecules (MHC I) antigen presentation pathway and cytotoxic T lymphocytes (CTLs) induction, has not been well studied. We hypothesized that micelle-tailored vaccine with multiple cascaded lysosomal responsive capabilities could accelerate lysosomal escape and enhance cancer immunotherapy. To test our hypothesis, we created a novel micellar cancer vaccine (ovalbumin-loaded pH/redox dual-sensitive micellar vaccine, OLM-D) by cleavable conjugation of an antigen with house-made amphiphilic poly(l-histidine)–poly(ethylene glycol) (PLH–PEG) in current study. OLM-D was supposed to achieve cascade cytosol delivery of ovalbumin through three steps in terms of (i) initial redox triggered ovalbumin release, (ii) promoted proton inflow and micelle disassembly, and (iii) speeded proton sponge effect and lysosome bulging/broke. Redox-sensitive antigen release and consequently accelerative OLM-D disassembly were confirmed by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS–PAGE), transmission electronic microscopy (TEM), particle sizes, zeta potentials, and in vitro Ova release evaluation. The speeded cytosol delivery of ovalbumin was visualized under a confocal laser scanning microscope (CLSM). The ability of OLM-D to increase the MHC I molecule combination rate and antigen cross-presentation efficiency was identified by antigen presentation assay and maturation assay in bone marrow-derived dendritic cells (BMDCs). In vivo, the capability of OLM-D to accumulate in draining lymph nodes (LNs) after injection was visualized by real-time near infrared fluorescence imaging (NIRF) and the distribution order in different LNs was first observed (a, d, c, b). Enhanced cancer immunity of OLM-D was confirmed by increased CD3+CD8+ T cell quantity, CD3+CD8+25D11.6+ T cells quantity, and IFN-γ, IL-2 secretion post subcutaneous or intraperitoneal injection (p < 0.05). Taken together, our results indicated that OLM-D provided a promising cascade cytosol delivery strategy, which held great potential to guide further design of nano-particulate cancer vaccines for efficient cancer immunotherapy.
Neurotransmitter-Loaded Nanocapsule Triggers On-Demand Muscle Relaxation in Living Organism
Duc Long Le - ,
Ferdinandus - ,
Chin Kiat Tnee - ,
T. Thang Vo Doan - ,
Satoshi Arai - ,
Madoka Suzuki - ,
Keitaro Sou *- , and
Hirotaka Sato *
This paper reports the on-demand artificial muscle relaxation using a thermosensitive liposome encapsulating γ-aminobutyric acid (GABA) inhibitory neurotransmitter. Muscle relaxation is not feasible in principle, although muscle contraction can be easily induced by electrical stimulation. Herein, thermosensitive liposomes (phase transition temperature = 40 °C) were synthesized to encapsulate GABA and were injected into a leg of a living beetle. The leg was wrapped around by a Ni–Cr wire heater integrated with a thermocouple to enable the feedback control and to manipulate the leg temperature. The injected leg was temporarily immobilized by heating it up to 45 °C. The leg did not swing even by electrically stimulating the leg muscle. Subsequently, the leg recovered to swing. The result indicates that GABA was released from liposomes and fed to the leg muscle, enabling temporal muscle relaxation.
Exploitation of Cationic Silica Nanoparticles for Bioprinting of Large-Scale Constructs with High Printing Fidelity
Mihyun Lee - ,
Kraun Bae - ,
Pierre Guillon - ,
Jin Chang - ,
Øystein Arlov - , and
Marcy Zenobi-Wong *
Three-dimensional (3D) bioprinting allows the fabrication of 3D structures containing living cells whose 3D shape and architecture are matched to a patient. The feature is desirable to achieve personalized treatment of trauma or diseases. However, realization of this promising technique in the clinic is greatly hindered by inferior mechanical properties of most biocompatible bioink materials. Here, we report a novel strategy to achieve printing large constructs with high printing quality and fidelity using an extrusion-based printer. We incorporate cationic nanoparticles in an anionic polymer mixture, which significantly improves mechanical properties, printability, and printing fidelity of the polymeric bioink due to electrostatic interactions between the nanoparticles and polymers. Addition of cationic-modified silica nanoparticles to an anionic polymer mixture composed of alginate and gellan gum results in significantly increased zero-shear viscosity (1062%) as well as storage modulus (486%). As a result, it is possible to print a large (centimeter-scale) porous structure with high printing quality, whereas the use of the polymeric ink without the nanoparticles leads to collapse of the printed structure during printing. We demonstrate such a mechanical enhancement is achieved by adding nanoparticles within a certain size range (<100 nm) and depends on concentration and surface chemistry of the nanoparticles as well as the length of polymers. Furthermore, shrinkage and swelling of the printed constructs during cross-linking are significantly suppressed by addition of nanoparticles compared with the ink without nanoparticles, which leads to high printing fidelity after cross-linking. The incorporated nanoparticles do not compromise biocompatibility of the polymeric ink, where high cell viability (>90%) and extracellular matrix secretion are observed for cells printed with nanocomposite inks. The design principle demonstrated can be applied for various anionic polymer-based systems, which could lead to achievement of 3D bioprinting-based personalized treatment.
Multivalent Antibody–Nanoparticle Conjugates To Enhance the Sensitivity of Surface-Enhanced Raman Scattering-Based Immunoassays
Miyeon Lee - ,
Hyeran Kim - ,
Eungwang Kim - ,
So Yeon Yi - ,
Seul Gee Hwang - ,
Siyeong Yang - ,
Eun-Kyung Lim - ,
Bongsoo Kim *- ,
Juyeon Jung *- , and
Taejoon Kang *
Multivalent immunoprobes can improve the sensitivity of biosensors because increased valency can strengthen the binding affinity between the receptor and target biomolecules. Here, we report surface-enhanced Raman scattering (SERS)-based immunoassays using multivalent antibody-conjugated nanoparticles (NPs) for the first time. Multivalent antibodies were generated through the ligation of Fab fragments fused with Fc-binding peptides to immunoglobulin G. This fabrication method is easy and fast because of the elimination of heterologous protein expression, high degrees of antibody modifications, and covalent chemical ligation steps. We constructed multivalent antibody–NP conjugates (MANCs) and employed them as SERS immunoprobes. MANCs improved the sensitivity of SERS-based immunoassays by 100 times compared to standard antibody–NP conjugates. MANCs will increase the feasibility of practical SERS-based immunoassays.
Highly Biocompatible, Fluorescence, and Zwitterionic Carbon Dots as a Novel Approach for Bioimaging Applications in Cancerous Cells
Smriti Sri - ,
Robin Kumar - ,
Amulya K. Panda - , and
Pratima R. Solanki *
Highly biocompatible, excellently photostable, nitrogen- and sulfur-containing novel zwitterionic carbon dots (CDs) were synthesized by microwave-assisted pyrolysis. The size of CDs were 2–5 nm, with an average size of 2.61 ± 0.7 nm. CDs were characterized by UV/vis spectroscopy, fluorescence spectroscopy, zeta potential, Fourier-transform infrared spectroscopy, X-ray diffraction, and time-resolved fluorescence spectroscopy. CDs were known to emit blue fluorescence when excited at 360 nm, that is, UV region, and emit in the blue region of visible spectrum, that is, at 443 nm. CDs showed excitation-independent photoluminescence behavior and were highly fluorescent even at lower concentration under UV light. These CDs were highly fluorescent in nature, with the quantum yield being as high as 80%, which is comparable to that of organic dyes. The CDs were further used to image two different oral cancer cell lines, namely, FaDu (human pharyngeal carcinoma) and Cal-27 (human tongue carcinoma). The cell viability assay demonstarted that CDs were highly biocompatible, which was further confirmed by the side scattering studies as no change in the granularity was observed even at the highest concentration of 1600 μg/mL. The generation of reactive oxygen species (ROS) was also investigated and negligible generaton of ROS was detected. In addition to that, the uptake phenomenon, cell cycle analysis, exocytosis, and cellular uptake at 4 °C and in the presence of ATP inhibitor were studied. It was found that CDs easily cross the plasma membrane without hampering the cellular integrity.
Adenosine-Related Compounds as an Enhancer for Peroxidase-Mimicking Activity of Nanomaterials: Application to Sensing of Heparin Level in Human Plasma and Total Sulfate Glycosaminoglycan Content in Synthetic Cerebrospinal Fluid
Jyun-Guo You - ,
Yen-Ting Wang - , and
Wei-Lung Tseng *
A variety of compounds, such as DNA and protein, have been demonstrated to be effective in suppressing the catalytic activity of peroxidase-like nanomaterials. However, little investigations have been conducted to discover new chemical compounds for amplifying the catalytic activity of peroxidase-mimicking nanomaterials. This study discloses that adenosine analogues were useful as a universal enhancer for peroxidase-mimicking nanomaterials in the hydrogen peroxide-mediated oxidation of amplex ultrared at neutral pH. The optimal adenosine analogues for improving the peroxidase-like performance of citrate-stabilized gold nanoparticles (Au NPs), citrate-capped platinum NPs, bovine serum albumin-encapsulated gold nanoclusters, and unmodified magnetite NPs were found to be adenosine diphosphate (ADP), ADP, ADP, and adenosine monophosphate, respectively. The results show that adenosine analogue-induced enhancement in the peroxidase-like activity of nanomaterials was heavily associated with the number of adsorbed adenosine analogues onto the nanomaterial surface. The analysis of ADP-modified Au NPs by electron paramagnetic resonance spectroscopy indicates that the adsorbed ADP molecules on the Au NP surface not only activated H2O2 but also strengthened the interaction between hydroxyl radicals and nanomaterials. By integrating the ADP-boosted catalytic activity of peroxidase-like Au NPs, surfen-triggered NP aggregation, and specific surfen-sulfated glycosaminoglycan (GAG) interaction, a turn-on fluorescent probe was constructed to quantify the heparin level in human plasma and total sulfate GAG content in synthetic cerebrospinal fluid.
Effect of a Controlled Release of Epinephrine Hydrochloride from PLGA Microchamber Array: In Vivo Studies
Olga A. Sindeeva *- ,
Olga I. Gusliakova - ,
Olga A. Inozemtseva - ,
Arkady S. Abdurashitov - ,
Ekaterina P. Brodovskaya - ,
Meiyu Gai - ,
Valery V. Tuchin - ,
Dmitry A. Gorin - , and
Gleb B. Sukhorukov *
This paper presents the synthesis of highly biocompatible and biodegradable poly(lactide-co-glycolide) (PLGA) microchamber arrays sensitive to low-intensity therapeutic ultrasound (1 MHz, 1–2 W, 1 min). A reliable method was elaborated that allowed the microchambers to be uniformly filled with epinephrine hydrochloride (EH), with the possibility of varying the cargo amount. The maximum load of EH was 4.5 μg per array of 5 mm × 5 mm (about 24 pg of EH per single microchamber). A gradual, spontaneous drug release was observed to start on the first day, which is especially important in the treatment of acute patients. Ultrasound triggered a sudden substantial release of EH from the films. In vivo real-time studies using a laser speckle contrast imaging system demonstrated changes in the hemodynamic parameters as a consequence of EH release under ultrasound exposure. We recorded a decrease in blood flow as a vascular response to EH release from a PLGA microchamber array implanted subcutaneously in a mouse. This response was immediate and delayed (1 and 2 days after the implantation of the array). The PLGA microchamber array is a new, promising drug depot implantable system that is sensitive to external stimuli.
Hybrid Alginate@TiO2 Porous Microcapsules as a Reservoir of Animal Cells for Cell Therapy
Grégory Leroux - ,
Myriam Neumann - ,
Christophe F. Meunier - ,
Antoine Fattaccioli - ,
Carine Michiels - ,
Thierry Arnould - ,
Li Wang *- , and
Bao-Lian Su *
The number of patients suffering from diseases linked with hormone deficiency (e.g., type 1 diabetes mellitus) has significantly increased in recent years. As organ transplantation presents its limits, the design of novel robust devices for cell encapsulation is of great interest. The current study reports the design of a novel hybrid alginate microcapsule reinforced by titania via a biocompatible synthesis from an aqueous stable titania precursor (TiBALDH) and a cationic polyamine (PDDAC) under mild conditions. The biocompatibility of this one-pot synthesis was confirmed by evaluation of the cytotoxicity of the precursor, additive, product, and by-product. The morphology, structure, and properties of the obtained hybrid microcapsule were characterized in detail. The microcapsule displayed mesoporous, which was a key parameter to allow the diffusion of nutrients and metabolites and to avoid the entry of immune defenders. The hybrid microcapsule also showed enhanced mechanical stability compared to the pure alginate microcapsule, making it an ideal candidate as a cell reservoir. HepG2 model cells encapsulated in the hybrid microcapsules remained intact for 43 days as highlighted by fluorescent viability probes, their oxygen consumption, and their albumin secretion. The study provides a significant progress in the conception of the robust and biocompatible reservoirs of animal cells for cell therapy.
Versatile Fabrication of Size- and Shape-Controllable Nanofibrous Concave Microwells for Cell Spheroid Formation
Sang Min Park - ,
Seong Jin Lee - ,
Jiwon Lim - ,
Bum Chang Kim - ,
Seon Jin Han - , and
Dong Sung Kim *
Although the microfabrication techniques for microwells enabled to guide physiologically relevant three-dimensional cell spheroid formation, there have been substantial interests to more closely mimic nano/microtopographies of in vivo cellular microenvironment. Here, we developed a versatile fabrication process for nanofibrous concave microwells (NCMs) with a controllable size and shape. The key to the fabrication process was the use of an array of hemispherical convex electrolyte solution drops as the grounded collector for electrospinning, which greatly improved the degree of freedom of the size, shape, and curvature of an NCM. A polymer substrate with through-holes was prepared for the electrolyte solution to come out through the hole and to naturally form a convex shape because of surface tension. Subsequent electrolyte-assisted electrospinning process enabled to achieve various arrays of NCMs of triangular, rectangular, and circular shapes with sizes ranging from 1000 μm down to 250 μm. As one example of biomedical applications, the formation of human hepatoma cell line (HepG2) spheroids was demonstrated on the NCMs. The results indicated that the NCM enabled uniform, size-controllable spheroid formation of HepG2 cells, resulting in 1.5 times higher secretion of albumin from HepG2 cells on the NCM on day 14 compared with those on a nanofibrous flat microwell as a control.
Synthesis of Chiral Carbo-Nanotweezers for Enantiospecific Recognition and DNA Duplex Winding in Cancer Cells
Indu Tripathi - ,
Santosh K. Misra - ,
Fatemeh Ostadhossein - ,
Indrajit Srivastava - , and
Dipanjan Pan *
Targeting the DNA of tumor cells with small molecules may offer effective clinical strategies for transcriptional inhibition. We unveil synthesis and characterization of ∼20 nm chiral carbon nanoparticles for enantiospecific recognition of DNA. Our approach inculcates chirality in carbon nanoparticles by controlled tethering of minor groove binders, i.e., Tröger’s base (TB). The chiral particles positively enriched the cellular nucleus in MCF-7 breast cancer cells, irrespective of the TB asymmetry tethered on the particle surface, but negatively induced chiral carbon nanoparticles exhibited improved efficiency at inhibiting cell growth. Further studies indicated that these chiral particles act as nanotweezers to perturb the genomic DNA and induce apoptosis cascade in cancer cells.
Precise Assembly of Genetically Functionalized Magnetosomes and Tobacco Mosaic Virus Particles Generates a Magnetic Biocomposite
Frank Mickoleit - ,
Klara Altintoprak - ,
Nana L. Wenz - ,
Reinhard Richter - ,
Christina Wege - , and
Dirk Schüler *
Magnetosomes represent magnetic nanoparticles with unprecedented characteristics. Both their crystal morphology and the composition of the enveloping membrane can be manipulated by genetic means, allowing the display of functional moieties on the particle surface. In this study, we explore the generation of a new biomaterial assembly by coupling magnetosomes with tobacco mosaic virus (TMV) particles, both functionalized with complementary recognition sites. TMV consists of single-stranded RNA encapsidated by more than 2100 coat proteins, which enable chemical modification via functional groups. Incubation of EmGFP- or biotin-decorated TMV particles with magnetosomes genetically functionalized with GFP-binding nanobodies or streptavidin, respectively, results in the formation of magnetic, mesoscopic, strand-like biocomposites. TMV facilitates the agglomeration of magnetosomes by providing a scaffold. The size of the TMV–magnetosome mesostrands can be adjusted by varying the TMV–magnetosome particle ratios. The versatility of this novel material combination is furthermore demonstrated by coupling magnetosomes and terminal, 5′-functionalized TMV particles with high molecular precision, which results in “drumstick”-like TMV–magnetosome complexes. In summary, our approaches provide promising strategies for the generation of new biomaterial assemblies that could be used as scaffold for the introduction of further functionalities, and we foresee a broad application potential in the biomedical and biotechnological field.
Tetrahedral DNA Nanostructure Promotes Endothelial Cell Proliferation, Migration, and Angiogenesis via Notch Signaling Pathway
Dan Zhao - ,
Mengting Liu - ,
Qianshun Li - ,
Xiaolin Zhang - ,
Changyue Xue - ,
Yunfeng Lin - , and
Xiaoxiao Cai *
The problem of tissue vascularization is one of the obstacles that currently restricts the application of tissue engineering products to the clinic. Achieving tissue vascularization and providing adequate nutrients for tissues are an urgent problem to build complex and effective tissue-engineered tissues and organs. Therefore, the aim of this study was to investigate the effect of tetrahedral DNA nanostructures (TDNs), a novel and biocompatible nanomaterial, on angiogenesis. The results showed that TDNs can enter into endothelial cells (ECs) and promote EC proliferation, migration, tube formation, and expressions of angiogenic growth factors at the concentration of 250 nmol L–1, which was accompanied by activation of the Notch signaling pathway. These results provided a theoretical basis for the further understanding and potential use of TDNs in tissue engineering vascularization.
Energy, Environmental, and Catalysis Applications
Covalent-Organic Frameworks Composed of Rhenium Bipyridine and Metal Porphyrins: Designing Heterobimetallic Frameworks with Two Distinct Metal Sites
Eric M. Johnson - ,
Ralf Haiges - , and
Smaranda C. Marinescu *
The incorporation of homogeneous catalysts for CO2 reduction into extended frameworks has been a successful strategy for increasing catalyst lifetime and activity, but the effects of the linkers on catalysis are underexplored. In this work, a novel rhenium bipyridine complex was synthesized for the purpose of designing a covalent-organic framework (COF) with both metalloporphyrin and metal bipyridine moieties. Investigation of the rhenium complex as a homogeneous catalyst shows a faradaic efficiency of 81(8)% for the electrocatalytic conversion of CO2 to CO upon the addition of methanol as the proton source. Treatment of the rhenium complex with tetra(4-aminophenyl)porphyrin under Schiff base conditions produces the desired COF, as indicated by powder X-ray diffraction (PXRD) studies. Metalation of the porphyrins was accomplished through postsynthetic modification with CoCl2 and FeCl3 metal precursors. The retention of the PXRD peaks and appearance of new Co and Fe peaks in the corresponding X-ray photoelectron spectroscopy spectra suggest the successful incorporation of a secondary metal site into the framework. Cyclic voltammetry measurements display increases in current densities when the atmosphere is changed from N2 to CO2. Controlled potential electrolyses show that the cobalt-postmetalated COF has the highest activity toward CO2 reduction, reaching a faradaic efficiency of 18(2)%.
Two-Dimensional WS2@Nitrogen-Doped Graphite for High-Performance Lithium Ion Batteries: Experiments and Molecular Dynamics Simulations
Tekalign Terfa Debela - ,
Young Rok Lim - ,
Hee Won Seo - ,
Ik Seon Kwon - ,
In Hye Kwak - ,
Jeunghee Park *- ,
Won Il Cho - , and
Hong Seok Kang *
As promising candidates for anode materials in lithium ion batteries (LIB), two-dimensional tungsten disulfide (WS2) and WS2@(N-doped) graphite composites were synthesized, and their electrochemical properties were comprehensibly studied in conjunction with calculations. The WS2 nanosheets, WS2@graphite, and WS2@N-doped graphite (N-graphite) exhibit outstanding cycling performance with capacities of 633, 780, and 963 mA h g–1, respectively. To understand their lithium storage mechanism, first-principles calculations involving a series of ab initio NVT–NPT molecular dynamics simulations were conducted. The calculated discharge curves for amorphous phase are well matched with the experimental ones, and the capacities reach 620, 743, and 915 mA h g–1 for WS2, WS2@graphite, and WS2@N-graphite, respectively. The large capacities of the two composites can be attributed to the tendency of W and Li atoms to interact with graphite, suppressing the formation of W metal clusters. In the case of WS2@N-graphite, vigorous amorphization of the N-graphite enhances the interaction of W and Li atoms with the fragmented N-graphite in such a way that unfavorable Li–W repulsion is avoided at very early stage of lithiation. As a result, the volume expansion in WS2@graphite and WS2@N-graphite is calculated to be remarkably small (only 6 and 44%, respectively, versus 150% for WS2). Therefore WS2@(N-)graphite composites are expected to be almost free of mechanical pulverization after repeated cycles, which makes them promising and excellent candidates for high-performance LIBs.
TiO Phase Stabilized into Freestanding Nanofibers as Strong Polysulfide Immobilizer in Li–S Batteries: Evidence for Lewis Acid–Base Interactions
Arvinder Singh - and
Vibha Kalra *
We report the stabilization of titanium monoxide (TiO) nanoparticles in nanofibers through electrospinning and carbothermal processes and their unique bifunctionality—high conductivity and ability to bind polysulfides—in Li–S batteries. The developed three-dimensional TiO/carbon nanofiber (CNF) architecture with the inherent interfiber macropores of nanofiber mats provides a much higher surface area (∼427 m2 g–1) and overcomes the challenges associated with the use of highly dense powdered Ti-based suboxides/monoxide materials, thereby allowing for high active sulfur loading among other benefits. The developed TiO/CNF-S cathodes exhibit high initial discharge capacities of ∼1080, ∼975, and ∼791 mAh g–1 at 0.1, 0.2, and 0.5 C rates, respectively, with long-term cycling. Furthermore, freestanding TiO/CNF-S cathodes developed with rapid sulfur melt infiltration (∼5 s) eradicate the need of inactive elements, viz., binders, additional current collectors (Al-foil), and additives. Using postmortem X-ray photoelectron spectroscopy and Raman analysis, this study is the first to reveal the presence of strong Lewis acid–base interaction between TiO (3d2) and Sx2– through the coordinate covalent Ti–S bond formation. Our results highlight the importance of developing Ti-suboxides/monoxide-based nanofibrous conducting polar host materials for next-generation Li–S batteries.
Architecture of Biomimetic Water Oxidation Catalyst with Mn4CaO5 Clusterlike Structure Unit
Zhibin Geng - ,
Yu Sun - ,
Yuan Zhang - ,
Yanxiang Wang - ,
Liping Li - ,
Keke Huang - ,
Xiyang Wang - ,
Jinghai Liu - ,
Long Yuan - , and
Shouhua Feng *
Mn4CaO5 cluster in green plant is considered as the ideal structure for water oxidation catalysis. However, this structure is difficult to be constructed in heterogeneous catalyst because of its distorted spatial structure and unique electronic state. Herein, we report the synthesis of two-dimensional biomimetic Ca–Mn–O catalyst with Mn4CaO5 clusterlike structure through ultrasonic-assisted reduction treatment toward Ca-birnessite. The synergistic effect between ultrasonic and reduction successfully reduced the Mn oxidation state in Ca-birnessite without breaking the structure of MnO2 monolayers, forming a regular two-dimensional structure with Mn4CaO5 cubanelike structure unit for the first time. The biomimetic catalyst shows a superior water oxidation activity (turnover frequency = 3.43 s–1), which is the best in manganese-based heterogeneous catalyst to date. This work provides a new strategy for the precise synthesis of specific structure and exhibits a great prospect of biomimic in heterogeneous catalyst.
Biomimetic Root-like TiN/C@S Nanofiber as a Freestanding Cathode with High Sulfur Loading for Lithium–Sulfur Batteries
Yaqi Liao - ,
Jingwei Xiang - ,
Lixia Yuan *- ,
Zhangxiang Hao - ,
Junfang Gu - ,
Xin Chen - ,
Kai Yuan - ,
Pramod K. Kalambate - , and
Yunhui Huang *
It is a tough issue to achieve high electrochemical performance and high sulfur loading simultaneously, which is of important significance for practical Li–S batteries applications. Inspired by the transportation system of the plant root in nature, a biomimetic root-like carbon/titanium nitride (TiN/C) composite nanofiber is designed as a freestanding current collector for the high sulfur loading cathode. Like the plant root which absorbs water and oxygen from soil and transfers them to the trunk and branches, the root-like TiN/C matrix provides high-efficiency polysulfide, electron, and electrolyte transfer for the redox reactions via its three-dimensional-porous interconnected structure. In the meantime, TiN can not only anchor the polysulfides via the polar Ti–S and N–S bond but also further facilitate the redox reaction because of its high catalytic effect. With 4 mg cm–2 sulfur loading, the TiN/C@S cathode delivers a high initial discharge capacity of 983 mA h g–1 at 0.2 C current density; after 300 charge/discharge cycles, the discharge capacity remains 685 mA h g–1, corresponding to a capacity decay rate of ∼0.1%. Even when the sulfur loading is increased to 10.5 mg cm–2, the cell still delivers a high capacity of 790 mA h g–1 and a decent cycle life. We believe that this novel biomimetic root-like structure can provide some inspiration for the rational structure design of the high-energy lithium–sulfur batteries and other composite electrode materials.
Enhanced Pyroelectric Catalysis of BaTiO3 Nanowires for Utilizing Waste Heat in Pollution Treatment
Jiang Wu - ,
Ni Qin *- ,
Baowei Yuan - ,
Enzhu Lin - , and
Dinghua Bao *
A novel catalytic effect of pyroelectric materials induced by a change in temperature, namely pyroelectric catalysis, was found to be attractive due to its ability to utilize waste heat in pollution treatment. In this work, the pyroelectric catalytic properties of BaTiO3 (BTO) nanowires synthesized by a template hydrothermal method have been thoroughly investigated. The nanowires with an elongated polar axis show a superior pyroelectric catalytic performance in comparison with the equiaxial nanoparticles. Our numerical simulation results with a finite element method indicate that the enhanced catalytic efficiency of BTO nanowires can be attributed to the higher pyroelectric potential. On the basis of the pyroelectric effect and our experimental results, a pyroelectric catalytic degradation mechanism has been proposed by taking into account the migration of charge carriers and the formation of reaction radicals. This study for enhancing the pyroelectric catalytic activity by using BTO nanowires may provide a facile, promising, and new reusable strategy for the catalytic degradation of organic dye pollutant by means of temperature variation. It is hoped that the present work gives a clear understanding of the mechanism of pyroelectric catalysis.
Hydrogenated Na2Ti3O7 Epitaxially Grown on Flexible N-Doped Carbon Sponge for Potassium-Ion Batteries
Peihao Li - ,
Wei Wang - ,
Sheng Gong - ,
Fan Lv - ,
Hanxin Huang - ,
Mingchuan Luo - ,
Yong Yang - ,
Chao Yang - ,
Jinhui Zhou - ,
Chang Qian - ,
Bin Wang - ,
Qian Wang - , and
Shaojun Guo *
With its inherent zig-zag layered structure and open framework, Na2Ti3O7 (NTO) is a promising anode material for potassium-ion batteries (KIBs). However, its poor electronic conductivity caused by large band gap (∼3.7 eV) usually leads to low-performance KIBs. In this work, we synthesize the fluff-like hydrogenated Na2Ti3O7 (HNTO) nanowires grown on N-doped carbon sponge (CS) as a binder-free and current-collector-free flexible anode for KIBs (denoted as HNTO/CS). High-resolution X-ray photoelectron spectroscopy (XPS) and electron spin-resonance spectroscopy (ESR) confirm the existence of Ti–OHs and O vacancies in HNTO. The first-principles calculation discloses that both Ti–OHs and O vacancies are equivalent to n-type doping because they can shift the Fermi level up to the conduction band, thus leading to a higher electronic conductivity and better performance for KIBs. In addition, the N-doped CS can further reinforce the conductivity and avoid the aggregation of HNTO nanowires during cycling. As a result, the as-made HNTO/CS can deliver a capacity of 107.8 mAh g–1 at 100 mA g–1 after 20 cycles, and keep the capacity of 90.9% and 82.5% after 200 and 1555 cycles, respectively, much better than the samples without hydrogenation treatment or N-doped CS and reported KTixOy-based materials. Our work highlights the importance of hydrogenation treatment and N-doped CS in enhancing the electrochemical property for KIBs.
Experimental and Computational Study of the Lithiation of Ba8AlyGe46–y Based Type I Germanium Clathrates
Andrew Dopilka - ,
Ran Zhao - ,
J. Mark Weller - ,
Svilen Bobev - ,
Xihong Peng - , and
Candace K. Chan *
In this work, we investigate the electrochemical properties of Ba8AlyGe46–y (y = 0, 4, 8, 12, 16) clathrates prepared by arc-melting. These materials have cage-like structures with large cavity volumes and can also have vacancies on the Ge framework sites, features which may be used to accommodate Li. Herein, a structural, electrochemical, and theoretical investigation is performed to explore these materials as anodes in Li-ion batteries, including analysis of the effect of the Al content and framework vacancies on the observed electrochemical properties. Single-crystal X-ray diffraction (XRD) studies indicate the presence of vacancies at the 6c site of the clathrate framework as the Al content decreases, and the lithiation potentials and capacities are observed to decrease as the degree of Al substitution increases. From XRD, electrochemical, and transmission electron microscopy analysis, we find that all of the clathrate compositions undergo two-phase reactions to form Li-rich amorphous phases. This is different from the behavior observed in Si clathrate analogues, where there is no amorphous phase transition during electrochemical lithiation nor discernible changes to the lattice constant of the bulk structure. From density functional theory calculations, we find that Li insertion into the three framework vacancies in Ba8Ge43 is energetically favorable, with a calculated lithiation voltage of 0.77 V versus Li/Li+. However, the calculated energy barrier for Li diffusion between vacancies and around Ba guest atoms is at least 1.6 eV, which is too high for significant room-temperature diffusion. These results show that framework vacancies in the Ge clathrate structure are unlikely to significantly contribute to lithiation processes unless the Ba guest atoms are absent, but suggest that guest atom vacancies could open diffusion paths for Li, allowing for empty framework positions to be occupied.
Atomic Layer Deposition of a Film of Al2O3 on Electrodeposited Copper Foams To Yield Highly Effective Oxygen Carriers for Chemical Looping Combustion-Based CO2 Capture
Nur Sena Yüzbasi - ,
Andac Armutlulu - ,
Paula M. Abdala - , and
Christoph R. Müller *
A rapid electrochemical deposition protocol is reported to synthesize highly porous Cu foams serving as model oxygen carriers for chemical looping, a promising technology to reduce anthropogenic CO2 emission. To overcome the sintering-induced decay in the oxygen carrying capacity of unsupported Cu foams, Al2O3 films of different thicknesses (0.1–25 nm) are deposited onto the Cu foams via atomic layer deposition (ALD). An ALD-grown Al2O3 overcoat of 20 nm thickness (∼4 wt % Al2O3) is shown to be sufficient to ensure excellent redox cyclic stability. Al2O3-coated Cu foams exhibit a capacity retention of 96% over 10 redox cycles, outperforming their coprecipitated counterpart (equal Al2O3 content). The structural evolution of the stabilized foams is probed in detail and compared to benchmark materials to elucidate the stabilizing role of the Al2O3 overcoat. Upon heat treatment, the initially conformal Al2O3 overcoat induces a fragmentation of large Cu(O) branches into small particles. After multiple redox cycles, the Al2O3 overcoat transforms into sub-micrometer-sized grains of aluminum-containing phases (δ-Al2O3, CuAl2O4, and CuAlO2) that are dispersed homogeneously within the CuO matrix. Finally, the diffusion of Cu through an Al2O3 layer upon heat treatment in an oxidizing atmosphere is probed in model thin films.
SnO2 Nanosheets Anchored on a 3D, Bicontinuous Electron and Ion Transport Carbon Network for High-Performance Sodium-Ion Batteries
Xun Zhao - ,
Ming Luo - ,
Wenxia Zhao - ,
Ruimei Xu - ,
Yong Liu *- , and
Hui Shen
Here, we demonstrate the in situ growth of SnO2 nanosheets on a freestanding carbonized eggshell membrane (CEM), which provides three-dimensional, bicontinuous electron and ion transport pathways through a massively interconnected carbon fiber skeleton and interpenetrated pore network, respectively. This CEM has other advantages such as the ability to alleviate mechanical stress during cycling as a buffer matrix. When used as an additive-free anode in a sodium-ion battery, SnO2 nanosheets can realize a complete electrochemical reaction and maintain good cycling stability with the help of a CEM. For instance, SnO2 nanosheets delivered a high reversible capacity of 656 mA h g–1 in the 5th cycle at 0.1 A g–1, approaching 98% of its theoretical specific capacity, and maintained a high reversible specific capacity of 420 mA h g–1 after 200 cycles at 0.2 A g–1.
L12 Atomic Ordered Substrate Enhanced Pt-Skin Cu3Pt Catalyst for Efficient Oxygen Reduction Reaction
Na Cheng - ,
Ling Zhang - ,
Shuying Mi - ,
Hao Jiang - ,
Yanjie Hu - ,
Haibo Jiang *- , and
Chunzhong Li *
Constructing Pt skin on intermetallics has been confirmed as an efficient strategy to boost oxygen reduction reaction (ORR) kinetics. However, there still lacks a systematic study on revealing the influence of low-Pt-content intermetallic substrates (L12-PtM3). In this paper, Pt skin-encapsulated low-Pt-mole-fraction L12 Cu3Pt has been constructed (denoted as Pt-o-Cu3Pt/C) and compared with its disordered analogue (denoted as Pt-d-Cu3Pt/C). The L12 substrate shows a contracted lattice structure and provides Pt-o-Cu3Pt/C with an excellent specific activity of 1.73 mA cm–2, which is 1.4- and 8.4-fold higher than that of Pt-d-Cu3Pt/C and commercial Pt/C, respectively. Density functional theory calculations reveal that this superior performance is attributed to the more favorable oxygen adsorption energy of surface Pt atoms. Furthermore, the lower formation energy of L12 Cu3Pt combined with the enhanced antioxygenation of Pt provide Pt-o-Cu3Pt/C with a superior durability, showing only a 12.5% loss in mass activity after 5000 potential cycles. Therefore, it is suggested that L12 atomic ordered structure with a low Pt fraction is a promising substrate for building high-performance Pt-skin catalysts for ORR.
Gas Phase Electrolysis of Carbon Dioxide to Carbon Monoxide Using Nickel Nitride as the Carbon Enrichment Catalyst
Pengfei Hou - ,
Xiuping Wang - ,
Zhuo Wang - , and
Peng Kang *
Nickel nitride was employed as the carbon enrichment electrocatalyst to reduce CO2 both in the aqueous phase and at the gas–solid interface. In an aqueous electrolyte, the CO Faradaic efficiency reached 85.7% at −0.90 V versus reversible hydrogen electrode with a partial current density of 6.3 mA cm–2. When gaseous CO2 was used as a reactant in a flow cell, the CO Faradaic efficiency increased to 92.5% and current density reached 23.3 mA cm–2. By contrast, metallic Ni and NiO generated predominantly H2. The increased amount of strong base sites in the Ni3N catalyst could enrich CO2 at the catalyst surface, and the utilization of gas phase electrolysis, has cooperatively enhanced reactivity.
Boosting Overall Water Splitting via FeOOH Nanoflake-Decorated PrBa0.5Sr0.5Co2O5+δ Nanorods
Zonghuai Zhang - ,
Beibei He *- ,
Liangjian Chen - ,
Huanwen Wang - ,
Rui Wang - ,
Ling Zhao - , and
Yansheng Gong *
The development of an efficient, robust, and low-cost catalyst for water electrolysis is critically important for renewable energy conversion. Herein, we achieve a significant improvement in electrocatalytic activity for both the oxygen-evolution reaction (OER) and the hydrogen-evolution reaction (HER) by constructing a novel hierarchical PrBa0.5Sr0.5Co2O5+δ (PBSC)@FeOOH catalyst. The optimized PBSC@FeOOH-20 catalyst consisted of layered perovskite PBSC nanorods and 20 nm thick amorphous FeOOH nanoflakes exhibiting an excellent electrocatalytic activity for the OER and the HER in 0.1 M KOH media, delivering a current density of 10 mA cm–2 at overpotentials of 390 mV for the OER and 280 mV for the HER, respectively. The substantially enhanced performance is probably attributed to the hierarchical nanostructure, the good charge-transfer capability, and the strong electronic interactions of FeOOH and PBSC. Importantly, an alkaline electrolyzer-integrated PBSC@FeOOH-20 catalyst as both the anode and cathode shows a highly active overall water splitting with a low voltage of 1.638 V at 10 mA cm–2 and high stability during continuous operation. This study provides new insights into exploring efficient bifunctional catalysts for overall water splitting, and it suggests that the rational design of the oxyhydroxide/perovskite heterostructure shows great potential as a promising type of electrocatalysts.
Scalable Ultrasonic Spray-Processing Technique for Manufacturing Large-Area CH3NH3PbI3 Perovskite Solar Cells
Li-Hui Chou - ,
Xiao-Feng Wang - ,
Itaru Osaka - ,
Chun-Guey Wu - , and
Cheng-Liang Liu *
Organic–inorganic hybrid perovskite solar cells are on the brink of a breakthrough in photovoltaic technology. Scale-up and large-area processing have become the focal points that must be resolved before commercialization. In this study, the scalable ultrasonic spray deposition method for high-throughput coating of the perovskite photoactive layer with a large active area of up to 3 cm2 is implemented by precisely controlling the concentration of the precursor solution and spray passes. CH3NH3PbI3 films with large crystallites and a suitable thickness of ∼350 nm are facilely developed through one-step direct ultrasonic spraying. Less hysteresis and highly reproducible power conversion efficiencies (PCEs) of up to 12.30% (11.43 ± 0.43% on average for 20 devices) are achieved by an optimized single-junction device with an active area of 1 cm2, along with good ambient stability. The device retained ∼80 and ∼65% of the initial PCE after 60 and 105 days in ambient, respectively. The ultrasonic spray-coated perovskite solar cells can be further scaled to larger areas of 2 and 3 cm2 and exhibit PCEs of 10.18 and 7.01%, respectively. The reliable scale-up process for manufacturing the atmospheric wet-coated perovskite film is available in cost-effective and easily operated bench-top variants to bridge the interconnection between applied research and industry.
Shape-Controlled Synthesis of Metal–Organic Frameworks with Adjustable Fenton-Like Catalytic Activity
Jiayi Liu - ,
Xuning Li - ,
Biao Liu - ,
Chunxiao Zhao - ,
Zhichong Kuang - ,
Ruisheng Hu - ,
Bin Liu *- ,
Zhimin Ao *- , and
Junhu Wang *
Controllable synthesis of metal–organic frameworks with well-defined morphology, composition, and size is of great importance toward understanding their structure–property relationship in various applications. Herein, we demonstrate a general strategy to modulate the relative growth rate of the secondary building units (SBUs) along different crystal facets for the synthesis of Fe–Co, Mn0.5Fe0.5–Co, and Mn–Co Prussian blue analogues (PBAs) with tunable morphologies. The same growth rate of SBUs along the {100}, {110}, and {111} surfaces at 0 °C results in the formation of spherical PBA particles, while the lowest growth rate of SBUs along the {100} surface resulting from the highest surface energy with increasing reaction temperature induces the formation of PBA cubes. Fenton reaction was used as the model reaction to probe the structure–catalytic activity relation for the as-synthesized catalysts. The cubic Fe–Co PBA was found to exhibit the best catalytic performance with reaction rate constant 6 times higher than that of the spherical counterpart. Via density functional theory calculations, the abundant enclosed {100} facets in cubic Fe–Co PBA were identified to have the highest surface energy and favor high Fenton reaction activity.
Compressible Supercapacitor with Residual Stress Effect for Sensitive Elastic-Electrochemical Stress Sensor
Ning Wei - ,
Limin Ruan - ,
Wei Zeng *- ,
Dong Liang *- ,
Chao Xu - ,
Linsheng Huang - , and
Jinling Zhao
In this work, we have synthesized graphene aerogels using natural-drying method and fabricated a compressible all-solid-state supercapacitor, which offers outstanding energy density of 23.08 Wh kg–1 at 240 W kg–1. We further demonstrate that the device is deformable in squeezed cases with a residual stress effect. Taking advantage of the compressibility and excellent electrochemical performance of the graphene aerogel, we offer a new type of stress sensor called elastic-electrochemical stress sensor. Served as the elastic-electrochemical stress device, the cell demonstrates steady response current toward the external mechanical force by transforming mechanical energy to electrochemical energy. The high-sensitive stress sensor will help us comprehend the interaction principle between electrochemistry and external stress well.
(111) Facets-Oriented Au-Decorated Carbon Nitride Nanoplatelets for Visible-Light-Driven Overall Water Splitting
Jiaxin Bai - ,
Baichuan Lu - ,
Qing Han *- ,
Quansong Li *- , and
Liangti Qu *
Development of a simple and stable photocatalyst for overall water splitting is a promising avenue for solar energy conversion. Here, carbon nitride (CN) nanosheet panels decorated with in situ-formed (111) facets-oriented Au nanoparticles (AuNPs) have been prepared by vapor-deposition polymerization followed by an easy immersion technique. Benefiting from the enhanced visible light absorption, the surface plasmon resonance effect of AuNPs, rapid transportation and separation of charge carriers, as well as better-aligned valence band levels, the as-obtained photocatalyst shows effective overall water splitting with stoichiometric H2 and O2 evolution even without any sacrificial agent, distinct from the half-reaction of Pt-decorated CN. This work opens up a brand-new route for facet self-selective growth of metal on two-dimensional conjugated carbon nitride materials, which has been demonstrated to be effective for artificial photosynthesis applications.
Giant Microgels with CO2-Induced On–Off, Selective, and Recyclable Adsorption for Anionic Dyes
Zanru Guo *- ,
Qiang Chen - ,
Hongjian Gu - ,
Zhanfeng He *- ,
Wenyuan Xu - ,
Jiali Zhang - ,
Yongxin Liu - ,
Leyan Xiong - ,
Longzhen Zheng - , and
Yujun Feng *
Adsorbents that are capable of controllable pollutants adsorption and release without secondary pollution are attractive in water treatment. Here, we propose eco-friendly CO2 as a trigger to switch the charge states and collapse–expansion transition of giant microgels consisting of hydrophilic acrylamide and hydrophobic 2-(diethylamino)ethyl methacrylate and demonstrated the on–off, selective, and recyclable adsorption of anionic dyes on microgels under CO2 stimulation. Apart from easy-handling separation from the water by a simple filtration process, the maximum adsorption capacity is as high as 821 mg g–1, and the adsorption isotherms and kinetics obeyed Langmuir isotherm and the pseudo-second-order kinetics models, respectively. The anionic dye can also be separated from the mixture solution using CO2-treated microgels. Moreover, a wastewater treatment prototype with microgel-packed column was fabricated. Under continuous flow condition, the dye was removed and recovered by alternative bubbling CO2 and flushing with aqueous alkali (pH 12). Thus, this type of microgels with CO2-induced protonation–deprotonation transition can serve as a cost-effective, environmentally friendly, and efficient adsorbent for water purification applications.
Ultraviolet Irradiation Treatment for Enhanced Sodium Storage Performance Based on Wide-Interlayer-Spacing Hollow C@MoS2@CN Nanospheres
Jingying Duan - ,
Guohui Qin *- ,
Luofu Min - ,
Yuchen Yang - , and
Chengyang Wang *
The photochemistry and sodium storage process have been generally considered as two separated approaches without strong connection. Here, ultraviolet (UV) irradiation was applied to sodium-ion batteries to improve the electrochemical performance of MoS2-based composites. C@MoS2@CN nanospheres consist of double protective structures, including inner hollow carbon spheres with a thin wall (C) and outer N-doping carbon nanosheets (CNs) derived from polydopamine. The special nanostructure possesses the virtues such as wide-interlayer spacing, flexible feature with great structure integrity, and rich active sites, which endow the fast electron transfer and shorten the ion diffusion pathways. Under the excitation of UV-light, intense electrons and holes are accumulated within MoS2-based composites. The excited electrons can promote the preinsertion of Na+. More importantly, dense electrons promote the electrolyte to decompose and hence form a stable solid electrolyte interphase in advance. After UV-light irradiation treatment in the electrolyte, the initial Coulombic efficiency of C@MoS2@CN electrodes increased from 48.2 to 79.6%, and benefiting from the fine nanostructure, the C@MoS2@CN electrode with UV irradiation treatment delivered a great rate performance 116 mAh g–1 in 20 s and super cycling stability that 87.6% capacity was retained after 500 cycles at 500 mA g–1. When employed as anode for sodium-ion hybrid capacitors, it delivered a maximum power density of 6.84 kW kg–1 (with 114.07 Wh kg−1 energy density) and a maximum energy density of 244.15 Wh g–1 (with 152.59 W kg–1 power density). This work sheds new viewpoints into the applications of photochemistry in the development of energy storage devices.
Restricting Growth of Ni3Fe Nanoparticles on Heteroatom-Doped Carbon Nanotube/Graphene Nanosheets as Air-Electrode Electrocatalyst for Zn–Air Battery
Chenglong Lai - ,
Jie Wang - ,
Wen Lei - ,
Cuijuan Xuan - ,
Weiping Xiao - ,
Tonghui Zhao - ,
Ting Huang - ,
Lingxuan Chen - ,
Ye Zhu - , and
Deli Wang *
Exploring bifunctional oxygen electrode catalysts with efficient and stable oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) performance is one of the limitations for high-performance zinc–air battery. In this work, Ni3Fe alloy nanoparticles incorporated in three-dimensional (3D) carbon nanotube (CNT)/graphene nanosheet composites with N and S codoping (Ni3Fe/N–S–CNTs) as bifunctional oxygen electrode electrocatalysts for zinc–air battery. The main particle size of Ni3Fe nanoparticles could be well restricted because of the unique 3D structure of carbon nanotube/graphene nanosheet composites (N–S–CNTs). The large specific area of N–S–CNTs is conducive to the uniform dispersion of Ni3Fe nanoparticles. On the basis of the synergistic effect of Ni3Fe nanoparticles with N–S–CNTs, and the sufficient exposure of reactive sites, the synthesized Ni3Fe/N–S–CNTs catalyst exhibits excellent OER performance with a low overpotential of 215 mV at 10 mA cm–2, and efficient ORR activity with a half-wave potential of 0.877 V. When used as an electrocatalyst in zinc–air battery, the device exhibits a power density of 180.0 mW cm–2 and long term durability for 500 h.
Superlithiated Polydopamine Derivative for High-Capacity and High-Rate Anode for Lithium-Ion Batteries
Xiaowan Dong - ,
Bing Ding - ,
Hongshuai Guo - ,
Hui Dou - , and
Xiaogang Zhang *
Organic electrode materials, with low-cost synthesis and environmental friendliness, have gained significant research interest in lithium-ion batteries (LIBs). Polydopamine (PDA), as a bioderived organic electrode material, exhibits a low capacity of ∼100 mAh g–1, greatly limiting the practical application in LIBs. In this work, we find that a simple heat treatment at 300 °C can endow PDA-derived material (PDA300) with superior electrochemical performance. The obtained PDA300 electrode exhibits an ultrahigh capacity of 977 mAh g–1 at 50 mA g–1. Further combining the PDA300 with highly conductive Ti3C2Tx MXene, the obtained PDA300/Ti3C2Tx composite is demonstrated by high capacity (1190 mAh g–1, 50 mA g–1), excellent rate capability (remaining 552 mAh g–1 at 5 A g–1), and good cycling stability (82% retaining after 1000 cycles). The outstanding lithium storage performance is highly associated with the superlithiation process of the unsaturated carbon–carbon bonds in the PDA derivative and the introduction of the highly conductive Ti3C2Tx substrate with a unique two-dimensional nanostructure. This work will provide new opportunities for the expansion of high-performance organic anodes for LIBs.
Studies on Catalytic Activity of Hydrogen Peroxide Generation according to Au Shell Thickness of Pd/Au Nanocubes
Inho Kim - ,
Myung-gi Seo - ,
Changhyeok Choi - ,
Jin Soo Kim - ,
Euiyoung Jung - ,
Geun-Ho Han - ,
Jae-Chul Lee - ,
Sang Soo Han - ,
Jae-Pyoung Ahn *- ,
Yousung Jung *- ,
Kwan-Young Lee *- , and
Taekyung Yu *
The catalytic properties of materials are determined by their electronic structures, which are based on the arrangement of atoms. Using precise calculations, synthesis, analysis, and catalytic activity studies, we demonstrate that changing the lattice constant of a material can modify its electronic structure and therefore its catalytic activity. Pd/Au core/shell nanocubes with a thin Au shell thickness of 1 nm exhibit high H2O2 production rates due to their improved oxygen binding energy (ΔEO) and hydrogen binding energy (ΔEH), as well as their reduced activation barriers for key reactions.
Boosted Performance of Ir Species by Employing TiN as the Support toward Oxygen Evolution Reaction
Guoqiang Li - ,
Kai Li - ,
Long Yang - ,
Jinfa Chang - ,
Rongpeng Ma - ,
Zhijian Wu - ,
Junjie Ge *- ,
Changpeng Liu - , and
Wei Xing *
Reducing the noble-metal loading without sacrificing the catalytic performance of the oxygen evolution reaction (OER) catalysts is paramount yet highly challenging. Herein, IrO2@Ir/TiN electrocatalysts employing TiN as the support have been developed and shown high efficiency toward OER. TiN is found not only to disperse the IrO2@Ir nanoparticles effectively but also to exert the electronic modulation of Ir by downshifting its d-band center of 0.21 eV compared to pure IrO2. Excitingly, TiN remarkably enhances the catalytic performance of Ir, where the overpotential to achieve the current density of 10 mA cm–2 is only 265 mV for the IrO2@Ir/TiN (60 wt %) catalyst. As a result, 71.7 wt % of the Ir metal can be saved to compare with the commercial Ir-black counterpart. Moreover, TiN can inhibit the aggregation and oxidative dissolution of Ir species, thereby enhancing the operational stability. The combined advantages of TiN open a new solution to reduce the anodic catalyst cost through boosting the catalytic activity and stability.
Zoom in Catalyst/Ionomer Interface in Polymer Electrolyte Membrane Fuel Cell Electrodes: Impact of Catalyst/Ionomer Dispersion Media/Solvent
Raghunandan Sharma *- and
Shuang Ma Andersen *
Large-scale applications of polymer electrolyte membrane fuel cells (PEMFCs) are throttled primarily by high initial cost and durability issues of the electrodes, which essentially consist of the nanoparticulate catalysts (e.g., Pt) having accessibility to electrons (e–), protons (H+), and fuel/oxidant through catalyst support, polymer electrolyte ionomer, and porous gas diffusion layer, respectively. Hence, to achieve high electrode performance in terms of activity and/or durability, understanding and optimization of the catalyst/support and catalyst/ionomer interfaces are of significant importance. Present study demonstrates an alternative route to inspect the catalyst/ionomer interface through an accelerated stress test combined with electrochemical impedance spectroscopy. Various interfaces are created through catalyst inks prepared using commercial Pt/C catalyst powder dispersed in different solvents. Electrode degradation pattern turns out to be a very useful tool to interpret a catalyst/ionomer interface structure. Variations of interfacial impedance, electrochemical surface area (ECSA), and double layer capacitance with the number of potential cycles suggested significant impact of catalyst/ionomer interface on the catalyst performance. A quantification of the degradation mechanisms responsible for ECSA loss during AST was employed to further understand the correlations between the electrochemical performance of the electrodes and their catalyst/ionomer interface structures. The knowledge may be implied to further optimize the electrode structure and hence to advance the PEMFC technology.
In Situ Formation of Isolated Bimetallic PtCe Sites of Single-Dispersed Pt on CeO2 for Low-Temperature CO Oxidation
Jing Li - ,
Yu Tang - ,
Yuanyuan Ma - ,
Zhiyun Zhang - ,
Franklin (Feng) Tao *- , and
Yongquan Qu *
Identification of the chemical states of catalytic sites is critical for an atomic-level understanding of catalytic mechanisms. Herein, hydrogen thermal pretreatment of the Pt single atoms on porous nanorods of CeO2 (Pt1/PN-CeO2) induced the formation of isolated bimetallic PtCe sites as a new type of active center for CO oxidation. The evolutions of Pt1/PN-CeO2 catalysts during the hydrogen pretreatment and CO oxidation were examined by various in situ techniques including infrared, ambient-pressure X-ray photoelectron and X-ray absorption spectroscopy. The experimental results demonstrate that these bimetallic sites can be partially preserved or reoxidized into Pt–O–Ce with a low coordination number with oxygen under realistic conditions, leading to the appropriate CO adsorption and activating the efficient activity of Pt1/PN-CeO2 for CO oxidation at low temperature.
High Capacity and Cycle-Stable Hard Carbon Anode for Nonflammable Sodium-Ion Batteries
Xingwei Liu - ,
Xiaoyu Jiang - ,
Ziqi Zeng - ,
Xinping Ai - ,
Hanxi Yang - ,
Faping Zhong *- ,
Yongyao Xia - , and
Yuliang Cao *
Nonflammable phosphate electrolytes are in principle able to build intrinsically safe Na-ion batteries, but their electrochemical incompatibility with anodic materials, especially hard carbon anode, restricts their battery applications. Here, we propose a new strategy to enable high-capacity utilization and cycle stability of hard carbon anodes in the nonflammable phosphate electrolyte by using low-cost Na+ salt with a high molar ratio of salt/solvent combined with an solid electrolyte interphase film-forming additive. As a result, the carbon anode in the trimethyl phosphate (TMP) electrolyte with a high molar ratio of [NaClO4]/[TMP] and 5% fluoroethylene carbonate additive demonstrates a high reversible capacity of 238 mAh g–1, considerable rate capability, and long-term cycling life with 84% capacity retention over 1500 cycles. More significantly, this work provides a promising route to build intrinsically safe and low-cost sodium-ion batteries for large-scale energy storage applications.
Grain Boundary Softening: A Potential Mechanism for Lithium Metal Penetration through Stiff Solid Electrolytes
Seungho Yu - and
Donald J. Siegel *
Models based on linear elasticity suggest that a solid electrolyte with a high shear modulus will suppress “dendrite” formation in batteries that use metallic lithium as the negative electrode. Nevertheless, recent experiments find that lithium can penetrate stiff solid electrolytes through microstructural features, such as grain boundaries. This failure mode emerges even in cases where the electrolyte has an average shear modulus that is an order of magnitude larger than that of Li. Adopting the solid-electrolyte Li7La3Zr2O12 (LLZO) as a prototype, here we demonstrate that significant softening in elastic properties occurs in nanoscale regions near grain boundaries. Molecular dynamics simulations performed on tilt and twist boundaries reveal that the grain boundary shear modulus is up to 50% smaller than in bulk regions. We propose that inhomogeneities in elastic properties arising from microstructural features provide a mechanism by which soft lithium can penetrate ostensibly stiff solid electrolytes.
Functional Inorganic Materials and Devices
Tunable Electrical and Optical Properties of Nickel Oxide (NiOx) Thin Films for Fully Transparent NiOx–Ga2O3 p–n Junction Diodes
Maria Isabel Pintor-Monroy - ,
Diego Barrera - ,
Bayron L. Murillo-Borjas - ,
Francisco Javier Ochoa-Estrella - ,
Julia W. P. Hsu - , and
Manuel A. Quevedo-Lopez *
One of the major limitations of oxide semiconductors technology is the lack of proper p-type materials to enable devices such as pn junctions, light-emitting diodes, and photodetectors. This limitation has resulted in an increased research focus on these materials. In this work, p-type NiOx thin films with tunable optical and electrical properties as well as its dependence with oxygen pressure during pulsed laser deposition are demonstrated. The control of NiOx films resistivity ranged from ∼109 to ∼102 Ω cm, showing a p-type behavior with Eg tuning from 3.4 to 3.9 eV. Chemical composition and the resulting band diagrams are also discussed. The all-oxide NiOx–Ga2O3 pn junction showed very low leakage current, an ideality factor of ∼2, 105 on/off ratio, and 0.6 V built-in potential. Its J–V temperature dependence is also analyzed. C–V measurements demonstrate diodes with a carrier concentration of 1015 cm–3 for the Ga2O3 layer, which is fully depleted. These results show a stable, promising diode, attractive for future photoelectronic devices.
Ultrasensitive 2D/3D Heterojunction Multicolor Photodetectors: A Synergy of Laterally and Vertically Aligned 2D Layered Materials
Jiandong Yao - ,
Zhaoqiang Zheng - , and
Guowei Yang *
In this work, a p-type 2D SnS nanofilm containing both laterally and vertically aligned components was successfully deposited on an n-type Si substrate through pulsed-laser deposition. Energy band analysis demonstrates a typical type-II band alignment between SnS and Si, which is beneficial to the separation of photogenerated carriers. The as-fabricated p-SnS/n-Si heterojunction photodetector exhibits multicolor photoresponse from ultraviolet to near-infrared (370–1064 nm). Importantly, the device manifests a high responsivity of 273 A/W, a large external quantum efficiency of 4.2 × 104%, and an outstanding detectivity of 7× 1013 Jones (1 Jones = 1 cm Hz1/2 W–1), which far outperforms state-of-the-art 2D/3D heterojunction photodetectors incorporating either laterally or vertically aligned 2D layered materials (2DLMs). The splendid performance is ascribed to lateral SnS’s dangling-bond-free interface induced efficient carrier separation, vertical SnS’s high-speed carrier transport, and collision ionization induced carrier multiplication. In sum, the current work depicts a unique landscape for revolutionary design and advancement of 2DLM-based heterojunction photodetectors.
Highly Efficient and Flexible Photosensors with GaN Nanowires Horizontally Embedded in a Graphene Sandwich Channel
Sangmoon Han - ,
Seoung-Ki Lee - ,
Ilgyu Choi - ,
Jihoon Song - ,
Cheul-Ro Lee - ,
Kangmin Kim - ,
Mee-Yi Ryu - ,
Kwang-Un Jeong - , and
Jin Soo Kim *
In this study, we report highly efficient and flexible photosensors with GaN nanowires (NWs) horizontally embedded in a graphene sandwich structure fabricated on polyethylene terephthalate. GaN NWs and the graphene sandwich structure are used as light-absorbing media and the channel for carrier movement, respectively. To form uniform high-quality crystalline GaN NWs on Si(111) substrates, the initial nucleation behavior of the NWs was manipulated by applying the new growth technique of Ga predeposition. High-resolution transmission electron microscopic images obtained along the vertical direction of GaN NWs showed that stacking faults, typically observed in Si-based (In,Ga)As NWs, were rare. Consequently, narrow and strong optical emission was observed from the GaN NWs at wavelengths of 365.12 nm at 300 K. The photocurrent and photoresponsivity of the flexible photosensor with 802 nm long GaN NWs horizontally embedded in the graphene sandwich channel were measured as 9.17 mA and 91.70 A/W, respectively, at the light intensity of 100 mW/cm2, which are much higher than those previously reported. The high optical-to-electrical conversion characteristics of our flexible photosensors are attributed to the increase in the effective interface between the light-absorbing media and the carrier channel by the horizontal distribution of the GaN NWs within the graphene sandwich structure. After 200 cyclic-bending test of the GaN NW photosensor at the strain of 3%, the photoresponsivity under strain was measured as 89.04 A/W at 100 mW/cm2, corresponding to 97.1% of the photoresponsivity obtained before bending. The photosensor proposed in this study is relatively simple in device design and fabrication, and it requires no sophisticated nanostructural design to minimize the resistance to metal contacts.
CsBr-Induced Stable CsPbI3–xBrx (x < 1) Perovskite Films at Low Temperature for Highly Efficient Planar Heterojunction Solar Cells
Zhenzhen Li - ,
Jia Xu *- ,
Shijie Zhou - ,
Bing Zhang - ,
Xiaolong Liu - ,
Songyuan Dai - , and
Jianxi Yao *
All-inorganic cesium lead perovskites have emerged as alternative absorbing layers in solar cells owing to their superb thermal stability compared with the organic–inorganic hybrid perovskites. However, the desired cubic CsPbI3 phase forms at a high temperature and suffers from a phase transition to the orthorhombic yellow phase at room temperature. A developed nonstoichiometric method is applied to fabricate CsPbI3–xBrx (x < 1) films by adding excess CsBr into the precursor solution. The excess CsBr in the precursor solution helps to produce a microstrain in the lattice to stabilize the cubic CsPbI3 phase at low temperature and incorporate a small part of Br– into the CsPbI3 lattice. At the optimal CsBr concentration (0.5 M), the corresponding solar cell achieves a power conversion efficiency of 10.92%. This work provides an effective way to stabilize the cubic CsPbI3–xBrx (x < 1) phase at low temperature to further improve the performance of all-inorganic perovskite solar cells.
Abrupt Thermal Shock of (NH4)2Mo3S13 Leads to Ultrafast Synthesis of Porous Ensembles of MoS2 Nanocrystals for High Gain Photodetectors
Saiful M. Islam - ,
Vinod K. Sangwan - ,
Yuan Li - ,
Joohoon Kang - ,
Xiaomi Zhang - ,
Yihui He - ,
Jing Zhao - ,
Akshay Murthy - ,
Shulan Ma - ,
Vinayak P. Dravid - ,
Mark C. Hersam - , and
Mercouri G. Kanatzidis *
Ultrafast synthesis of high-quality transition-metal dichalcogenide nanocrystals, such as molybdenum disulfide (MoS2), is technologically relevant for large-scale production of electronic and optoelectronic devices. Here, we report a rapid solid-state synthesis route for MoS2 using the chemically homogeneous molecular precursor, (NH4)2Mo3S13·H2O, resulting in nanoparticles with estimated size down to 25 nm only in 10 s at 1000 °C. Despite the extreme nonequilibrium conditions, the resulting porous MoS2 nanoparticles remain aggregated to preserve the form of the original rod shape bulk morphology of the molecular precursor. This ultrafast synthesis proceeds through the rapid decomposition of the precursor and rearrangement of Mo and S atoms coupled with simultaneous efficient release of massive gaseous species, to create nanoscale porosity in the resulting isomorphic pseudocrystals, which are composed of the MoS2 nanoparticles. Despite the very rapid escape of massive amounts of NH3, H2O, H2S, and S gases from the (NH4)2Mo3S13·H2O mm sized crystals, they retain their original shape as they convert to MoS2 rather than undergo explosive destruction from the rapid escape process of the gases. The obtained pseudocrystals are made of aggregated MoS2 nanocrystals exhibit a Brunauer–Emmett–Teller surface area of ∼35 m2/g with an adsorption average pore width of ∼160 Å. The nanoporous MoS2 crystals are solution processable by dispersing in ethanol and water and can be cast into large-area uniform composite films. Photodetectors fabricated from these films show more than 2 orders of magnitude higher conductivity (∼6.25 × 10–6 S/cm) and photoconductive gain (20 mA/W) than previous reports of MoS2 composite films. The optoelectronic properties of this nanoporous MoS2 imply that the shallow defects that originate from the ultrafast synthesis act as sensitizing centers that increase the photocurrent gain via two-level recombination kinetics.
Anatase TiO2—A Model System for Large Polaron Transport
Bixing Yan - ,
Dongyang Wan *- ,
Xiao Chi - ,
Changjian Li - ,
Mallikarjuna Rao Motapothula - ,
Sonu Hooda - ,
Ping Yang - ,
Zhen Huang - ,
Shengwei Zeng - ,
Akash Gadekar Ramesh - ,
Stephen John Pennycook - ,
Andrivo Rusydi - ,
Ariando *- ,
Jens Martin *- , and
Thirumalai Venkatesan *
Large polarons have been of significant recent technological interest as they screen and protect electrons from point-scattering centers. Anatase TiO2 is a model system for studying large polarons as they can be studied systematically over a wide range of temperature and carrier density. The electronic and magneto transport properties of reduced anatase TiO2 epitaxial thin films are analyzed considering various polaronic effects. Unexpectedly, with increasing carrier concentration, the mobility increases, which rarely happens in common metallic systems. We find that the screening of the electron–phonon (e–ph) coupling by excess carriers is necessary to explain this unusual dependence. We also find that the magnetoresistance could be decomposed into a linear and a quadratic component, separately characterizing the carrier transport and trapping as a function of temperature, respectively. The various transport behaviors could be organized into a single phase diagram, which clarifies the evolution of large polaron in this material.
Synergy between Isomorphous Acid and Basic Metal–Organic Frameworks for Anhydrous Proton Conduction of Low-Cost Hybrid Membranes at High Temperatures
Xi-Yan Dong - ,
Jun-Hao Wang - ,
Shan-Shan Liu - ,
Zhen Han - ,
Qing-Jie Tang - ,
Fei-Fei Li *- , and
Shuang-Quan Zang *
Metal–organic frameworks (MOFs) embedded in polymer have showed efficiency in improving proton conduction of hybrid membranes under hydrated conditions. However, anhydrous proton conduction of such hybrid membranes over 100 °C remains great challenge. Here, proton conductive hybrid membranes combined acid group (−SO3H)- and basic group (−NH2)-modified isomorphous MOFs, namely UiO-66(SO3H) (abbreviated as A, the initial of acid) and UiO-66(NH2) (abbreviated as B, the initial of basic) and a low-cost polymer (chitosan, CS) were prepared. The proton conductivity of the optimum dual MOF-cofilled hybrid membranes (CS/A + B) reached 3.78 × 10–3 S/cm at 120 °C and under anhydrous conditions, under which each component, that is MOF A, MOF B and CS, and single MOF-filled hybrid membranes (CS/A and CS/B) nearly lost proton conduction without exception, producing unprecedented results of one plus one more greater than two. The synergistic effects among UiO-66(SO3H), UiO-66(NH2), and CS on improving conductivity are also observed under hydrated conditions, the highest proton conductivity of CS/A + B reached 5.2 × 10–2 S/cm, which is 1.86, compared to that of the pure CS membrane at 100 °C and 98% relative humidity. The anhydrous proton conductivity of CS/A + B over 100 °C is one of the highest for MOF-based hybrid membranes. MOFs and hybrid membranes were extensively characterized and the proton conductive mechanism was revealed. The achievements open a new avenue for MOF-based anhydrous proton-conducting membranes and would advance the exploration of future application of these MOFs in fuel cells.
Nanoscale Electrochemical Phenomena of Polarization Switching in Ferroelectrics
Anton V. Ievlev *- ,
Chance C. Brown - ,
Joshua C. Agar - ,
Gabriel A. Velarde - ,
Lane W. Martin - ,
Alex Belianinov - ,
Petro Maksymovych - ,
Sergei V. Kalinin - , and
Olga S. Ovchinnikova *
Polarization switching is a fundamental feature of ferroelectric materials, enabling a plethora of applications and captivating the attention of the scientific community for over half a century. Many previous studies considered ferroelectric switching as a purely physical process, whereas polarization is fully controlled by the superposition of electric fields. However, screening charge is required for thermodynamic stability of the single domain state that is of interest in many technological applications. The screening process has always been assumed to be fast; thus, the rate-limiting phenomena were believed to be domain nucleation and domain wall dynamics. In this manuscript, we demonstrate that polarization switching under an atomic force microscopy tip leads to reversible ionic motion in the top 3 nm of PbZr0.2Ti0.8O3 surface layer. This evidence points to a strong chemical component to a process believed to be purely physical and has major implications for understanding ferroelectric materials, making ferroelectric devices, and interpreting local ferroelectric switching.
Anti-Site Defects-Assisted Enhancement of Electrogenerated Chemiluminescence from in Situ Mn2+-Doped Supertetrahedral Chalcogenide Nanoclusters
Feng Wang - ,
Jian Lin - ,
Shansheng Yu - ,
Xiaoqiang Cui *- ,
Asghar Ali - ,
Tao Wu - , and
Yang Liu *
Understanding and revealing the connection between defects and dopant for improving electrogenerated chemiluminescence (ECL) efficiency remain a constant challenge. In this work, the in situ Mn2+-doped Mn1.36Zn5.64In28S56 supertetrahedral chalcogenide semiconductor nanoclusters (NCs) with an ECL efficiency as high as 27.1% was obtained, the corresponding ECL behaviors were investigated, and the vital role of more anti-site defects (ADs) introduced in situ on the ECL emission was elucidated. The ADs can not only give rise to the ECL emission peak at 494 nm but also assist transfer of electrons to induce and enhance the ECL emission at 627 nm from doped Mn2+ in the NCs. Furthermore, based on the fact that dissolved oxygen can enhance the ECL intensity, a highly sensitive ECL sensor for the determination of dissolved oxygen was developed. This insight into the fundamental interactions between Mn2+ dopants and defects in NC host may open new opportunities for the design of novel ECL materials to promote their application potential in electrochemical analysis and imaging.
Oxygen Vacancy Ordering Modulation of Magnetic Anisotropy in Strained LaCoO3–x Thin Films
Ningbin Zhang - ,
Yinlian Zhu *- ,
Da Li - ,
Desheng Pan - ,
Yunlong Tang - ,
Mengjiao Han - ,
Jinyuan Ma - ,
Bo Wu - ,
Zhidong Zhang - , and
Xiuliang Ma
Oxygen vacancy configurations and concentration are coupled with the magnetic, electronic, and transport properties of perovskite oxides, and manipulating the physical properties by tuning the vacancy structures of thin films is crucial for applications in many functional devices. In this study, we report a direct atomic resolution observation of the preferred orientation of vacancy ordering structure in the epitaxial LaCoO3–x (LCO) thin films under various strains from large compressive to large tensile strain utilizing scanning transmission electron microscopy (STEM). Under compressive strains, the oxygen vacancy ordering prefers to be along the planes parallel to the heterointerface. Changing the strains from compressive to tensile, the oxygen vacancy planes turn to be perpendicular to the heterointerface. Aberration-corrected STEM images, electron diffractions, and X-ray diffraction combined with X-ray photoelectron spectroscopy demonstrate that the vacancy concentration increases with increasing misfit strains and vacancy distribution is more ordered and homogeneous. The temperature-dependent magnetization curves show the Curie temperature increases, displaying a positive correlation with the misfit strains. With change in the strain from compressive to tensile, anisotropy fields vary and show large values under tensile strains. It is proposed that oxygen vacancy concentration and preferred ordering planes are responsible for the enhanced magnetic properties of LCO films. Our results have realized a controllable preparation of oxygen vacancy ordering structures via strains and thus provide an effective method to regulate and optimize the physical properties such as magnetic properties by strain engineering.
Killing Two Birds with One Stone: Coating Ag NPs Embedded Filter Paper with Chitosan for Better and Durable Point-of-Use Water Disinfection
Meikun Fan *- ,
Lin Gong - ,
Ji Sun - ,
Dongmei Wang - ,
Feng Bi - , and
Zhengjun Gong *
In this study, porous chitosan (CS) coated Ag NPs embedded filter paper (CAEFP) was fabricated for point-of-use water disinfection application. Thanks for the presence of CS coating, the tensile strength of the CAEFP in wet condition was found to be 1.8 MPa, 700% increase compared with where there was no CS coating, making it much more durable. In addition, the coating with CS could greatly boost the Ag NPs loading without worrying about the excessive release of Ag into the treated water, thereby significantly improving the bactericidal efficiency but still be safe to drink in terms of Ag release. Furthermore, by controlling the amount of CS used, the flow rate and bactericidal efficiency of the CAEFP could be manipulated (customized). When the CS content increased from 0.5 to 2.0 wt %, the flow rate of CAEFP would drop from 9.3 to 0.53 L/min/m2, and the bactericidal efficiency against Escherichia coli and Bacillus subtilis could improve from 4 and 3.6 to 4.9 and 4.8 log reduction, respectively. At optimum condition, the total Ag in treated water by CAEFP was below 45 μg/L, only 1/10 of that from Ag NPs loaded filter paper without CS coating, half of the WHO drinking water requirement (<100 μg/L). Natural surface water samples were used for the demonstration of the bactericidal performance of the CAEFP. Both the total bacterial and E. coli counts met the WHO standard.
Effect of Controlled-Atmosphere Storage and Ethanol Rinsing on NaNi0.5Mn0.5O2 for Sodium-Ion Batteries
Lituo Zheng - ,
Lingjun Li - ,
Ramesh Shunmugasundaram - , and
M.N. Obrovac *
NaNi0.5Mn0.5O2 is a promising sodium-ion battery cathode material that has been extensively studied. However, the air sensitivity of this material limits practical application and is not well understood. Here, we present a detailed study of NaNi0.5Mn0.5O2 powders stored in different atmospheres (oxygen, argon, and carbon dioxide), either dry or wet. X-ray diffraction and Fourier transform infrared measurements were used to characterize the materials and their surface species before and after controlled-atmosphere storage. It was determined that the exposure of untreated NaNi0.5Mn0.5O2 powders to moisture results in desodiation and material degradation, leading to poor cycling. This effect was found to be caused by reactive surface species. From these results, a simple ethanol washing method was found to significantly reduce the air-reactivity and improve the electrochemical performance of NaNi0.5Mn0.5O2 by removing surface impurities formed by air exposure.
Carbon Composite Networks with Ultrathin Skin Layers of Graphene Film for Exceptional Electromagnetic Interference Shielding
Xiaohui Ma - ,
Yang Li - ,
Bin Shen *- ,
Lihua Zhang - ,
Zeping Chen - ,
Yinfeng Liu - ,
Wentao Zhai *- , and
Wenge Zheng
Natural cotton was selected as a cheap and renewable carbon source to fabricate novel carbon networks with porous three-dimensional conductive frameworks composed of numerous unique hollow carbon fibers by pyrolysis, and outstanding electromagnetic interference (EMI) shielding effectiveness (SE) of ∼26.9–46.9 dB was observed for the samples (∼0.3 mm in thickness) with density of ∼0.14–0.06 g/cm3. Moreover, the combination of cotton-derived carbon networks with graphene through the construction of a sandwich configuration, where graphene sheets were dispersed inhomogeneously on both sides of carbon networks, was further developed and the resultant carbon composite networks with ultrathin skin layers of graphene film in thickness of only ∼2 μm possessed higher EMI SE of ∼48.5–87.0 dB than that (∼33.7–55.6 dB) of pure carbon networks in thickness of ∼0.3–0.7 mm, possibly due to the enhanced EM reflection and absorption of EM waves penetrating the material. The SE increment of ∼26–41% was also observed in the sandwiched samples in comparison with the counterparts with homogeneous graphene dispersion, demonstrating a very promising configuration for the significant SE enhancement.
Consecutive Junction-Induced Efficient Charge Separation Mechanisms for High-Performance MoS2/Quantum Dot Phototransistors
Sangyeon Pak - ,
Yuljae Cho - ,
John Hong - ,
Juwon Lee - ,
Sanghyo Lee - ,
Bo Hou - ,
Geon-Hyoung An - ,
Young-Woo Lee - ,
Jae Eun Jang - ,
Hyunsik Im - ,
Stephen M. Morris - ,
Jung Inn Sohn *- ,
SeungNam Cha *- , and
Jong Min Kim
This publication is Open Access under the license indicated. Learn More
Phototransistors that are based on a hybrid vertical heterojunction structure of two-dimensional (2D)/quantum dots (QDs) have recently attracted attention as a promising device architecture for enhancing the quantum efficiency of photodetectors. However, to optimize the device structure to allow for more efficient charge separation and transfer to the electrodes, a better understanding of the photophysical mechanisms that take place in these architectures is required. Here, we employ a novel concept involving the modulation of the built-in potential within the QD layers for creating a new hybrid MoS2/PbS QDs phototransistor with consecutive type II junctions. The effects of the built-in potential across the depletion region near the type II junction interface in the QD layers are found to improve the photoresponse as well as decrease the response times to 950 μs, which is the faster response time (by orders of magnitude) than that recorded for previously reported 2D/QD phototransistors. Also, by implementing an electric-field modulation of the MoS2 channel, our experimental results reveal that the detectivity can be as large as 1 × 1011 jones. This work demonstrates an important pathway toward designing hybrid phototransistors and mixed-dimensional van der Waals heterostructures.
All-Dielectric Surface-Enhanced Infrared Absorption-Based Gas Sensor Using Guided Resonance
Yuhua Chang - ,
Dihan Hasan - ,
Bowei Dong - ,
Jingxuan Wei - ,
Yiming Ma - ,
Guangya Zhou - ,
Kah Wee Ang - , and
Chengkuo Lee *
The surface-enhanced infrared absorption (SEIRA) technique has been focusing on the metallic resonator structures for decades, exploring different approaches to enhance sensitivity. Although the high enhancement is achieved, the dissipative loss and strong heating are the intrinsic drawbacks of metals. Recently, the dielectric platform has emerged as a promising alternative. In this work, we report a guided resonance-based all-dielectric photonic crystal slab as the platform for SEIRA. The guided resonance-induced enhancement in the effective path length and electric field, together with gas enrichment polymer coating, leads to a detection limit of 20 ppm in carbon dioxide (CO2) sensing. This work explores the feasibility to apply low loss all-dielectric structures as a surface enhancement method in the transmission mode.
Organic Electronic Devices
Improved Room Temperature NO2 Sensing Performance of Organic Field-Effect Transistor by Directly Blending a Hole-Transporting/Electron-Blocking Polymer into the Active Layer
Shijiao Han - ,
Zuchong Yang - ,
Zongkang Li - ,
Xinming Zhuang - ,
Deji Akinwande *- , and
Junsheng Yu *
Over the past decades, organic field-effect transistor (OFET) gas sensors have maintained a rapid development. However, the majority of OFET gas sensors show insufficient detection capability towards oxidizing gases such as nitrogen oxide, compared with the inorganic counterpart. In this paper, a new strategy of OFET nitrogen dioxide (NO2) gas sensor, consisting of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(9-vinylcarbazole) (PVK) blend, is reported. Depending on the gate voltage, this sensor can operate in two modes at room temperature. Of the two modes exposed to NO2 for 5 min, when the gate voltage is 0 V, the highest NO2 responsivity of this OFET is >20 000% for 30 ppm (≈700% for 600 ppb) with the 1:1 P3HT/PVK blend, it is ≈40 times greater than that with the pure P3HT. The limit of detection of ≈300 ppb is achieved, and there is still room for improvement. While in the condition of −40 V, the response increases by 15 times than that with the pure P3HT. This is the first attempt to improve the OFET sensing performance using PVK, which usually functions as a hole-transport layer in the light- emitting device. The enhancement of sensing performance is attributed to the aggregation-controlling and hole-transporting/electron-blocking effect of PVK. This work demonstrates that the hole-transport material can be applied to improve the NO2 sensor with simple solution process, which expands the material choice of OFET gas sensors.
Role of Bimolecular Exciton Kinetics in Controlling the Efficiency of Organic Light-Emitting Diodes
Amrita Dey - and
Dinesh Kabra *
Here, we have carried out a spectroscopic investigation on the operational organic light-emitting diodes (OLEDs) to determine the role of emission layer thickness on the optoelectronic performance of OLEDs based on a poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) copolymer system. Our study shows that delayed fluorescence (DF) via triplet–triplet annihilation (TTA) contributes significantly to boost the OLED efficiency through its fractional contribution. Interestingly, we note that DF contribution varies as a function of the emissive layer thickness. From the time-resolved electroluminescence (TREL) and triplet absorption (under electrical excitation) studies, we have seen that the emissive layer thickness controls triplet exciton generation and decay processes. From TREL, we have also shown that singlet–triplet annihilation (STA) is the dominant fluorescence quenching mechanism in bulk of the emissive layer, whereas thinner devices have significant exciton quenching at the interface of the injection layer/F8BT. The strength of STA differs in thin versus thick samples, which has been correlated with the spectral & spatial overlap integral of singlet and triplet states. Hence, STA strength and triplet population density are critical parameters for an explanation of high efficiency in unusually thick F8BT OLEDs.
Visible-Light-Responsive High-Detectivity Organic Photodetectors with a 1 μm Thick Active Layer
Jong Baek Park - ,
Jong-Woon Ha - ,
Sung Cheol Yoon - ,
Changjin Lee - ,
In Hwan Jung *- , and
Do-Hoon Hwang *
Organic photodetectors (OPDs) are attracting attention for use in flexible and portable electronic applications such as image sensors, remote sensing, optical communications, and medical sensors because of their strong photon responsivity in thin films over a broad range of wavelengths. In particular, the efficient photon-to-current conversion of OPDs under visible light allows their use in indirect X-ray detectors using scintillators to convert X-rays to visible light. The polymer poly(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-5-(2-hexyldecyl)-1,3-bis(6-octylthieno[3,2-b]thiophen-2-yl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione) (PBDTT-8ttTPD) shows strong absorption bands in the region of 500–650 nm, as well as high hole mobility, which provides excellent photoresponsivity and photon-to-current conversion efficiency. A p–n junction photodetector was fabricated by blending PBDTT-8ttTPD and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) and varying the thickness of the active layer (260–1100 nm). The PBDTT-8ttTPD:PC71BM-based OPDs show promising photodetecting properties having a low dark current of 3.72 × 10–9 A cm–2 and high responsivity of 0.39 A W–1 because of the well-controlled morphology, high molar absorption coefficient, and excellent carrier mobility of the PBDTT-8ttTPD:PC71BM layer. Consequently, the specific detectivity of the PBDTT-8ttTPD-based OPD devices was 1.13 × 1013 Jones at −2 V on irradiation with a light-emitting diode (530 nm wavelength) with a power density of 55.6 μW cm–2.
High-Performance All-Polymer Solar Cells with a High Fill Factor and a Broad Tolerance to the Donor/Acceptor Ratio
Xiaohui Liu - ,
Yang Zou - ,
Hai-Qiao Wang - ,
Lei Wang - ,
Junfeng Fang *- , and
Chuluo Yang *
Manipulating the donor/acceptor (D/A) weight ratio is a critical route to produce highly efficient polymer solar cells (PSCs). However, most of the reported device performances are strongly sensitive to the blend ratio. In this work, highly efficient all-PSCs based on PBDB-T:N2200 active layer have been achieved, presenting impressive photovoltaic performance with high tolerance to wide D/A ratios ranging from 1:1 to 9:1, thus providing a broad blend ratio processing window for future practical production. In particular, the optimal device delivers the champion power conversion efficiency (PCE) of 8.61% with an outstanding fill factor (FF) of up to 75.4%, which is one of the highest FF values for the reported binary all-PSCs. Comprehensive morphological, electrical, and mechanism analysis together pointed out that the remarkable device performance are derived from the favorable interpenetrating network morphology, efficient exciton generation/dissociation, well-balanced carrier transport, and reduced bimolecular recombination. Moreover, compared to the small molecule-based and fullerene-based PSC counterparts, the all-PSCs demonstrate an excellent resilience to the D/A ratio, maintaining over 50% of the maximum PCE at a ratio of 49:1 with an extremely low acceptor content. These results depict a bright prospect of the developed all-PSCs for promising applications as flexible and scalable optoelectronic devices.
Functional Nanostructured Materials (including low-D carbon)
Mechanics of Emulsion Electrospun Porous Carbon Fibers as Building Blocks of Multifunctional Materials
Yijun Chen - ,
Jizhe Cai - ,
James G. Boyd - ,
William Joshua Kennedy - , and
Mohammad Naraghi *
Many multifunctional composite structures incorporate porosity at various length scales to increase the available surface area of a functional component. One material system of particular interest is activated or porous carbon fibers and nanofibers that can serve as structural reinforcement as well as providing active surface for added functionality. A key question in the design and manufacture of these fibers is to what degree the induced pore affects the mechanical properties by inducing discontinuities in the material. To address this problem, mechanics of porous carbon nanofibers (CNFs) was studied for the first time as a function of their porous structure. Hollow CNF with porous shell was prepared by coaxial electrospinning a polyacrylonitrile/poly(methyl methacrylate) (PMMA) blend shell with a PMMA core. PMMA was removed by thermal decomposition during pyrolysis to form pores. Solid-shell CNF was prepared as a control with no PMMA in the shell. Results show that the modulus and strength of the porous-shell CNF with a porosity of 19.2 ± 1.3% were 65.0 ± 6.2 and 1.28 ± 0.14 GPa respectively, 13.9 ± 2.1% and 35.5 ± 4.9% lower than those of the solid-shell CNF. Finite-element analysis models were developed to decouple the effect of stress concentration and reduced load-bearing area in porous CNFs on their mechanical properties. The model predictions were in general agreement with the experimental results and were used to identify the most critical parameters that can affect load bearing in porous nanofibers. Considering the comparison of the experimental and modeling results, the intrinsic material strength (of the solid parts) does not seem to be affected by inducing pores; thus, fiber and pore geometries might be developed where the load paths are designed for even less of a strength loss.
Spatially and Precisely Controlled Large-Scale and Persistent Optical Gating in a TiOx–MoS2 Heterostructure
Po-Hsun Ho *- ,
Yi-Siang Shih - ,
Min-Ken Li - ,
Tzu-Pei Chen - ,
Fu-Yu Shih - ,
Wei-Hua Wang - , and
Chun-Wei Chen *
Optical gating derived from persistent photodoping is a promising technique that can control the transport behavior of two-dimensional (2D) materials through light modulation. The advantage of photoinduced doping is that the doping can be controlled precisely and spatially by tuning the light intensity and position. As most photoinduced doping methods suffer from a low doping level, persistent, strong photodoping was conducted in this study in TiOx–MoS2 heterostructures under ultraviolet (UV) illumination, which precisely controlled the doping to a high level (1.5 × 1013 cm–2) with a trap-mediated mechanism. This mechanism was confirmed by controlling the doping level with various UV pretreatment doses. After photodoping, devices displayed superior mobility, which is a characteristic of the modulation doping used in high-electron-mobility transistors. The modulation doping sites in the inner TiOx layer were far from the channel surface (MoS2); thus, the channel was able to preserve its high-mobility property even after doping. This dose-dependent, strong, and persistent photodoping phenomenon can render the TiOx–MoS2 heterostructure suitable for use in UV detectors and in nonvolatile light-driven memory products. Moreover, by using spatially controlled light scans, selective photodoping at the contact edges can dramatically reduce the contact resistance without destroying the on–off ratio of the device by forming an n+–n–n+ channel. Because TiOx–MoS2 heterostructures are versatile, they provide a compelling platform for high-performance 2D optoelectronic devices.
Sensitive and Robust Ultraviolet Photodetector Array Based on Self-Assembled Graphene/C60 Hybrid Films
Shuchao Qin - ,
Xiaoqing Chen - ,
Qianqian Du - ,
Zhonghui Nie - ,
Xinran Wang - ,
Hai Lu - ,
Xizhang Wang - ,
Kaihui Liu - ,
Yongbing Xu - ,
Yi Shi - ,
Rong Zhang *- , and
Fengqiu Wang *
Graphene has been widely investigated for use in high-performance photodetectors due to its broad absorption band and high carrier mobility. While exhibiting remarkably strong absorption in the ultraviolet range, the fabrication of a large-scale integrable, graphene-based ultraviolet photodetector with long-term stability has proven to be a challenge. Here, using graphene as a template for C60 assembly, we synthesized a large-scale all-carbon hybrid film with inherently strong and tunable UV aborption. Efficient exciton dissociation at the heterointerface and enhanced optical absorption enables extremely high photoconductive gain, resulting in UV photoresponsivity of ∼107 A/W. Interestingly, due to the electron–hole recombination process at the heterointerface, the response time can be modulated by the gate voltage. More importantly, the use of all-carbon hybrid materials ensures robust operation and further allows the demonstration of an exemplary 5 × 5 (2-dimensional) photodetector array. The devices exhibit negligible degradation in figures of merit even after 2 month of operation, indicating excellent environmental robustness. The combination of high responsivity, reliability, and scalable processability makes this new all-carbon film a promising candidate for future integrable optoelectronics.
Highly Efficient and Environmentally Stable Flexible Color Converters Based on Confined CH3NH3PbBr3 Nanocrystals
Andrea Rubino - ,
Miguel Anaya - ,
Juan F. Galisteo-López - ,
T. Cristina Rojas - ,
Mauricio E. Calvo *- , and
Hernán Míguez *
In this work, we demonstrate a synthetic route to attain methylammonium lead bromide (CH3NH3PbBr3) perovskite nanocrystals (nc-MAPbBr3, 1.5 nm < size < 3 nm) and provide them with functionality as highly efficient flexible, transparent, environmentally stable, and adaptable color-converting films. We use nanoparticle metal oxide (MOx) thin films as porous scaffolds of controlled nanopores size distribution to synthesize nc-MAPbBr3 through the infiltration of perovskite liquid precursors. We find that the control over the reaction volume imposed by the nanoporous scaffold gives rise to a strict control of the nanocrystal size, which allows us to observe well-defined quantum confinement effects on the photo-emission, being the luminescence maximum tunable with precision between λ = 530 nm (green) and λ = 490 nm (blue). This hybrid nc-MAPbBr3/MOx structure presents high mechanical stability and permits subsequent infiltration with an elastomer to achieve a self-standing flexible film, which not only maintains the photo-emission efficiency of the nc-MAPbBr3 unaltered but also prevents their environmental degradation. Applications as adaptable color-converting layers for light-emitting devices are envisaged and demonstrated.
High-Performance Flexible In-Plane Micro-Supercapacitors Based on Vertically Aligned CuSe@Ni(OH)2 Hybrid Nanosheet Films
Jiangfeng Gong *- ,
Jing-Chang Li - ,
Jing Yang - ,
Shulin Zhao - ,
Ziyuan Yang - ,
Kaixiao Zhang - ,
Jianchun Bao - ,
Huan Pang *- , and
Min Han *
The orientation and hybridization of ultrathin two-dimensional (2D) nanostructures on interdigital electrodes is vital for developing high-performance flexible in-plane micro-supercapacitors (MSCs). Despite great progress has been achieved, integrating CuSe and Ni(OH)2 nanosheets to generate advanced nanohybrids with oriented arrangement of each component and formation of porous frameworks remains a challenge, and their application for in-plane MSCs has not been explored. Herein, the vertically aligned CuSe@Ni(OH)2 hybrid nanosheet films with hierarchical open channels are skillfully deposited on Au interdigital electrodes/polyethylene terephthalate substrate via a template-free sequential electrodeposition approach, and directly employed to construct in-plane MSCs by choosing polyvinyl alcohol–LiCl gel as both the separator and the solid electrolyte. Because of the unique geometrical structure and combination of intrinsically conductive CuSe and battery-type Ni(OH)2 components, such hybrid nanosheet films can not only resolve the poor conductivity and re-stacking problems of Ni(OH)2 nanosheets but also create the 3D electrons or ions transport pathway. Thus, the in-plane MSCs device fabricated by such hybrid nanosheet films exhibits high volumetric specific capacitance (38.9 F cm–3). Moreover, its maximal energy and power density can reach 5.4 mW h cm–3 and 833.2 mW cm–3, superior to pure CuSe nanosheets, and most of reported carbon materials and metal hydroxides/oxides/sulfides based in-plane MSCs ones. Also, the hybrid nanosheet films device shows excellent cycling performance, good flexibility, and mechanical stability. This work may shed some light on optimizing 2D electrode materials and promote the development of flexible in-plane MSCs or other energy storage systems.
Carbon Nanotubes Grown on Graphite Films as Effective Interface Enhancement for an Aluminum Matrix Laminated Composite in Thermal Management Applications
Jing Chang - ,
Qiang Zhang *- ,
Yingfei Lin - ,
Chang Zhou - ,
Wenshu Yang - ,
Liwen Yan *- , and
Gaohui Wu
Uniform and dense carbon nanotubes (CNTs) were grown on the surface of the graphite film (GF) by a plasma-enhanced chemical vapor deposition process. The synthesized CNTs can act as a bridge between GF and Al matrix to enhance the interface performance and improve thermal properties of the GF/Al laminated composite simultaneously. A layer-by-layer CNTs–GF/Al composite with both increased mechanical property and thermal management capability was fabricated through an optimized pressure infiltration process, which was time- and energy-saving. The results show that the interface of the laminated composite is well bonded and no interface product such as Al4C3 is generated. Additional investigations reveal that the growth of CNTs is an effective way to improve the thermal conductivity and reduce the coefficient of thermal expansion of the GF reinforced Al composites. Overall, the best-performing CNTs–GF/Al composites with a CNTs–GF volume fraction of 51.42% show an increase of 47.99% in thermal conductivity and 26.44% in interlaminar shear strength, making them promising thermal management laminated materials.
Printed Nanocomposite Energy Harvesters with Controlled Alignment of Barium Titanate Nanowires
Mohammad H. Malakooti - ,
Florian Julé - , and
Henry A. Sodano *
Piezoelectric nanocomposites are commonly used in the development of self-powered miniaturized electronic devices and sensors. Although the incorporation of one-dimensional (1D) piezoelectric nanomaterials (i.e., nanowires, nanorods, and nanofibers) in a polymer matrix has led to the development of devices with promising energy harvesting and sensing performance, they have not yet reached their ultimate performance due to the challenges in fabrication. Here, a direct-write additive manufacturing technique is utilized to facilitate the fabrication of spatially tailored piezoelectric nanocomposites. High aspect ratio barium titanate (BaTiO3) nanowires (NWs) are dispersed in a polylactic acid (PLA) solution to produce a printable piezoelectric solution. The BaTiO3 NWs are arranged in PLA along three different axes of alignment via shear-induced alignment during a controlled printing process. The result of electromechanical characterizations shows that the nanowire alignment significantly affects the energy harvesting performance of the nanocomposites. The optimal power output can be enhanced by as much as eight times for printed nanocomposites with a tailored architecture of the embedded nanostructures. This power generation capacity is 273% higher compared to conventional cast nanocomposites with randomly oriented NWs. The findings of this study suggest that 3D printing of nanowire-based nanocomposites is a feasible, scalable, and rapid methodology to produce high-performance piezoelectric transducers with tailored micro- and nanostructures. This study offers the first demonstration of nanocomposite energy harvesters with spatially controlled filler orientation realized directly from a digital design.
Laser-Induced Dewetting of Metal Thin Films for Template-Free Plasmonic Color Printing
Harim Oh - ,
Jeeyoung Lee - ,
Minseok Seo - ,
In Uk Baek - ,
Ji Young Byun - , and
Myeongkyu Lee *
Plasmonic color laser printing has several advantages over pigment-based technology, including the absence of ink and toner and the production of nonfading colors. However, the current printing method requires a template that should be prepared via nanofabrication processes, making it impractical for large-area color images. In this study, we show that laser-induced dewetting of metal thin films by a nanosecond pulsed laser can be effectively utilized for plasmonic color printing. Ag, Au, and their complex films deposited on a glass substrate were dewetted into different surface structures such as droplets, rods, and ripples, depending on the incident laser energy. The resulting morphological evolutions could be explained by Rayleigh and capillary instabilities. For a bimetallic film comprising Ag nanowires coated on a Au layer, a few different plasmonic colors were generated from a single sample simply by changing the laser fluence. This provides a possible method for implementing plasmonic color laser printing without using a prepatterned template.
Marine-Biomass-Derived Porous Carbon Sheets with a Tunable N-Doping Content for Superior Sodium-Ion Storage
Yaqi Guo - ,
Wei Liu *- ,
Ruitao Wu - ,
Lanju Sun - ,
Yuan Zhang - ,
Yongpeng Cui - ,
Shuang Liu - ,
Huanlei Wang - , and
Baohong Shan
Synthesis of the electrode materials of sodium-ion storage devices from sustainable precursors via green methods is highly desirable. In this work, we fabricated a unique N, O dual-doped biocarbon nanosheet with hierarchical porosity by direct pyrolysis of low-cost cuttlebones and simple air oxidation activation (AOA) technique. With prolonging AOA time, thickness of the carbon sheets could be reduced controllably (from 35 to 5 nm), which may lead to tunable preparation of carbon nanosheets with a certain thickness. Besides, an unexpected increase in N-doping amount from 7.5 to 13.9 atom % was observed after AOA, demonstrating the unique role of AOA in tuning the doped heteroatoms of carbon matrix. This was also the first example of increasing N-doping content in carbons by treatment in air. More importantly, by optimizing the thickness of carbon sheets and heteroatom doping via AOA, superior sodium capacity–cycling retention–rate capability combinations were achieved. Specifically, a current state-of-the-art Na+ storage capacity of 640 mAh g–1 was obtained, which was comparable with the lithium-ion storage in carbon materials. Even after charging/discharging at large current densities (2 and 10 A g–1) for 10 000 cycles, the as-obtained samples still retained the capacities of 270 and 138 mAh g–1, respectively, with more than 90% retention. The assembled sodium-ion capacitors also delivered a high integrated energy–power density (36 kW h kg–1 at an ultrahigh power density of 53 000 W kg–1) and good cycling stability (90.5% of capacitance retention after 8000 cycles at 5 A g–1).
Bias- and Gate-Tunable Gas Sensor Response Originating from Modulation in the Schottky Barrier Height of a Graphene/MoS2 van der Waals Heterojunction
Hiroshi Tabata *- ,
Yuta Sato - ,
Kouhei Oi - ,
Osamu Kubo - , and
Mitsuhiro Katayama
We report on the gas-sensing characteristics of a van der Waals heterojunction consisting of graphene and a MoS2 flake. To extract the response actually originating from the heterojunction area, the other gas-sensitive parts were passivated by gas barrier layers. The graphene/MoS2 heterojunction device demonstrated a significant change in resistance, by a factor of greater than 103, upon exposure to 1 ppm NO2 under a reverse-bias condition, which was revealed to be a direct reflection of the modulation of the Schottky barrier height at the graphene/MoS2 interface. The magnitude of the response demonstrated strong dependences on the bias and back-gate voltages. The response further increased with increasing reverse bias. Conversely, it dramatically decreased when measured at a large forward bias or a large positive back-gate voltage. These behaviors were analyzed using a metal–semiconductor–metal diode model consisting of graphene/MoS2 and counter Ti/MoS2 Schottky diodes.
Applications of Polymer, Composite, and Coating Materials
Designing Novel Poly(oxyalkylene)-Segmented Ester-Based Polymeric Dispersants for Efficient TiO2 Photoanodes of Dye-Sensitized Solar Cells
Yow-An Leu - ,
Yen-An Lu - ,
Min-Hsin Yeh *- ,
Po-Ta Shih - ,
Sheng-Yen Shen - ,
Kuo-Chuan Ho *- , and
Jiang-Jen Lin *
A family of new polymeric dispersants, branched poly(oxyethylene)-segmented esters of trimellitic anhydride adduct (polyethylene glycol–trimethylolpropane–trimellitic anhydride, designated as PTT), were synthesized and utilized to homogeneously disperse TiO2 nanoparticles. The weight fraction of poly(oxyethylene)-segment in the dispersants and the molecular architecture in favoring the branched shape are two predominant factors for designing the effective dispersants. In particular, the poly(oxyethylene) block of 1000 g/mol from PEG1000 as the starting material and a total molecular weight of 12 000 g/mol have constituted the polymeric dispersants for the best performance for homogenizing TiO2 nanoparticles. The dispersant structures were characterized by using Fourier-transform infrared spectroscopy, acid value determination, and gel permeation chromatography. The TiO2 dispersibility was evaluated by dynamic light scattering and transmission electron microscopy. The synthesized dispersants were utilized to homogenize the as-prepared TiO2, further fabricated into films of photoanodes for dye-sensitized solar cells (DSSCs). The ultimate performance of DSSC was measured to be 8.17 ± 0.13% for the device efficiency (η) which was significantly higher than the conventional TiO2 photoanode at η = 7.14 ± 0.12%. The photoanode film was characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area, and dye-loading amount measurements. The kinetics of photogenerated electron in the photoanode, including electron lifetime and electron transit time of the film, was studied via electrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy, and intensity-modulated photovoltage spectroscopy.
Ultrabroadband Three-Dimensional Printed Radial Perfectly Symmetric Gradient Honeycomb All-Dielectric Dual-Directional Lightweight Planar Luneburg Lens
Jin Chen - ,
Xujin Yuan *- ,
Mingji Chen - ,
Xiaodong Cheng - ,
Anxue Zhang - ,
Gantao Peng - ,
Wei-Li Song *- , and
Daining Fang
An ultrabroadband all-dielectric planar Luneburg lens has been designed and fabricated in this study, which is in the form of a radial gradient lightweight honeycomb column. Because of the novel design of a radial symmetric honeycomb-like microstructure in the subwavelength dimension and the radial gradient configuration according to the refractive index distribution of Luneburg lens, the present lens can focus incident plane waves on the opposite side with high convergence, and its operating frequency range is rather broadband, spanning from 6 to 16 GHz. Besides, the all-dielectric honeycomb-like lens is lightweight with a mass density of 0.23 g/cm3, and its broadband transmittance is higher than the reported cases consisting of metallic metamaterial or gradient photonic crystal structures. A prototype of the lens is fabricated by using 3D printing techniques, on which the electric near-field distribution and far-field radiation pattern measurements have been carried out, and the aforementioned performances were demonstrated experimentally. It was also observed that for two point sources placed at the edge of the lens whose intersection angle with the center of the lens is 90°, the far-field radiation pattern was still kept highly directional, which means that the lens can generate two highly directional beams simultaneously, and is an efficient double input-double output device.
Scalable Fabrication of Thermally Insulating Mechanically Resilient Hierarchically Porous Polymer Foams
Ali Rizvi - ,
Raymond K. M. Chu - , and
Chul B. Park *
The requirement of energy efficiency demands materials with superior thermal insulation properties. Inorganic aerogels are excellent thermal insulators, but are difficult to produce on a large-scale, are mechanically brittle, and their structural properties depend strongly on their density. Here, we report the scalable generation of low-density, hierarchically porous, polypropylene foams using industrial-scale foam-processing equipment, with thermal conductivity lower than that of commercially available high-performance thermal insulators such as superinsulating Styrofoam. The reduction in thermal conductivity is attributed to the restriction of air flow caused by the porous nanostructure in the cell walls of the foam. In contrast to inorganic aerogels, the mechanical properties of the foams are less sensitive to density, suggesting efficient load transfer through the skeletal structure. The scalable fabrication of hierarchically porous polymer foams opens up new perspectives for the scalable design and development of novel superinsulating materials.
Transport Properties of Perfluorosulfonate Membranes Ion Exchanged with Cations
Jing Peng *- ,
Kun Lou - ,
Gabriel Goenaga - , and
Thomas Zawodzinski *
In this work, the properties of univalent, that is, Li+, Na+, NH4+, and TEA+ form perfluorosulfonate (PFSA) membranes are studied and compared to the properties of H+ form materials. Properties of these polymer membranes including water uptake, density and conductivity, were investigated for membranes exposed to various water activity levels. The water uptake by the membranes decreased in the order H+ > Li+ > Na+ > NH4+ > TEA+, the same order as the hydration enthalpy (absolute values) of cations. Conductivity values did not strictly follow this order, indicating the importance of different factors besides the hydration level. The partial molar volume of water is derived from the density data as a function of water content for the various membrane forms. This provides further insight into the water, cation, and polymer interactions. Factors that contribute to the conductivity of these membranes include the size of cations, the electrostatic attraction between cations and sulfonate group, and the ion-dipole and hydrogen bonding interactions between cations and water. NH4+ transport is surprisingly high given the low water uptake in NH4+ form membranes. We attribute this to the ability of this ion to develop hydrogen bonded structures that helps to overcome electrostatic interactions with sulfonates. Pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) was used to measure the diffusion coefficient of water in the membranes. FT-IR spectroscopy is employed to probe cation interactions with water and sulfonate sites in the polymer. Overall, the results reflect a competition between the strong electrostatic interaction between cation and sulfonate versus hydration and hydrogen bonding which vary with cation type.
Fluorescent Probes for Sugar Detection
Danielle Bruen - ,
Colm Delaney *- ,
Dermot Diamond - , and
Larisa Florea
Herein, a new class of polymerizable boronic acid (BA) monomers are presented, which are used to generate soft hydrogels capable of accurate determination of saccharide concentration. By exploiting the interaction of these cationic BAs with an anionic fluorophore, 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (pyranine), a two-component sugar-sensing system was realized. In the presence of such cationic BAs (o-BA, m-BA, and p-BA), the fluorescence of pyranine becomes quenched because of the formation of a nonfluorescent BA–fluorophore complex. Upon addition of saccharides, formation of a cyclic boronate ester results in dissociation of the nonfluorescent complex and recovery of the pyranine fluorescence. The response of this system was examined in solution with common monosaccharides, such as glucose, fructose, and galactose. Subsequent polymerization of the BA monomers yielded cross-linked hydrogels which showed similar reversible recovery of fluorescence in the presence of glucose.
Intrinsic Tuning of Poly(styrene–butadiene–styrene)-Based Self-Healing Dielectric Elastomer Actuators with Enhanced Electromechanical Properties
Christopher Ellingford - ,
Runan Zhang - ,
Alan M. Wemyss - ,
Christopher Bowen - ,
Tony McNally - ,
Łukasz Figiel - , and
Chaoying Wan *
The electromechanical properties of a thermoplastic styrene–butadiene–styrene (SBS) dielectric elastomer was intrinsically tuned by chemical grafting with polar organic groups. Methyl thioglycolate (MG) reacted with the butadiene block via a one-step thiol–ene “click” reaction under UV at 25 °C. The MG grafting ratio reached 98.5 mol % (with respect to the butadiene alkenes present) within 20 min and increased the relative permittivity to 11.4 at 103 Hz, with a low tan δ. The actuation strain of the MG-grafted SBS dielectric elastomer actuator was 10 times larger than the SBS-based actuator, and the actuation force was 4 times greater than SBS. The MG-grafted SBS demonstrated an ability to achieve both mechanical and electrical self-healing. The electrical breakdown strength recovered to 15% of its original value, and the strength and elongation at break recovered by 25 and 21%, respectively, after 3 days. The self-healing behavior was explained by the introduction of polar MG groups that reduce viscous loss and strain relaxation. The weak CH/π bonds through the partially charged (δ+) groups adjacent to the ester of MG and the δ- center of styrene enable polymer chains to reunite and recover properties. Intrinsic tuning can therefore enhance the electromechanical properties of dielectric elastomers and provides new actuator materials with self-healing mechanical and dielectric properties.
Designing pH-Responsive Biodegradable Polymer Coatings for Controlled Drug Release via Vapor-Based Route
Xiao Shi - ,
Yumin Ye *- ,
Hui Wang - ,
Fu Liu - , and
Zhijie Wang
We present the design of a novel pH-responsive drug release system that is achieved by solventless encapsulation of drugs within a microporous membrane using a thin capping layer of biodegradable poly(methacrylic anhydride) (PMAH) coating. The coating was synthesized via a mild vapor polymerization process, namely, initiated chemical vapor deposition, which allowed perfect retention of the anhydride groups during deposition. The synthesized polyanhydride underwent degradation upon exposure to aqueous buffers, resulting in soluble poly(methacrylic acid). The degradation behavior of PMAH is highly pH-dependent, and the degradation rate under pH 10 is 15 times faster than that under pH 1. The release profile of a model drug rifampicin clearly exhibited two stages: the initial stage when the coatings were being degraded but the drugs were well stored and the second stage when drugs were gradually exposed to the medium and released. The drug release also showed strong pH responsiveness where the duration of the initial stage under pH 1 was more than 7 and 3 times longer than that under pH 10 and 7.4, respectively, and the release rates at pH 7.4 and 10 were significantly faster than that at pH 1. The pH-dependent degradation of the encapsulant thus enabled good preservation of drugs under low-pH environment but high drug release efficiency under neutral and alkaline environment, suggesting potential applications in site-specific drug delivery systems.
Biomimetic Structural Color Films with a Bilayer Inverse Heterostructure for Anticounterfeiting Applications
Yao Meng - ,
Jinjing Qiu - ,
Suli Wu - ,
Benzhi Ju - ,
Shufen Zhang - , and
Bingtao Tang *
The unique brilliant and angle-independent structural colors of morpho butterfly wings were derived from the multilayer interference, diffraction, and scattering of light with a composite structure including ordered and quasiamorphous arrays. Inspired by the biological heterostructure of ordered and quasiamorphous arrays in the wings, a bilayer inverse heterostructure (BLIHS) containing ordered array layers inverse structure (OALIS) and quasiamorphous array layers inverse structure (Q-AALIS) of polyvinylidene fluoride were successfully prepared through the template method. The BLIHS films selectively displayed iridescent structural color derived from Bragg diffraction of OALIS, whereas the color states transform to noniridescent color because of Q-AALIS just by rotating the sample. Furthermore, the patterning process could be realized by using the spray-coating method on the BILIS films as quasiamorphous array layers. By virtue of this novel photonic structure, the switch between hiding and displaying patterns could be easily realized by changing the viewing angles, and the as-prepared films exhibited inherent excellent durability, which is crucial to their potential for practical applications as anticounterfeiting materials.
Fabrication of Air-Stable and Conductive Silk Fibroin Gels
Meng Yao - ,
Dihan Su - ,
Wenqi Wang - ,
Xin Chen - , and
Zhengzhong Shao *
Owing to their promising applications in flexible electronics, researchers have extensively explored flexible and conductive gels. However, these gels have unsatisfactory strength and flexibility as well as easily dry in air. Herein, a rationally designed robust regenerated silk fibroin (RSF)-based gel with significant flexibility and strength, favorable conductivity, and excellent air stability is fabricated by inducing the conformation transition of RSF from random coil to β-sheet in ionic liquid (IL)/water mixtures. We found that such RSF-based gels have a unique homogeneous network structure of RSF nanofibers, which is likely formed because of evenly distributed cross-links dominated by small-sized β-sheet domains created during the conformation transition of RSF. Although the unique homogeneous nanostructure/network contributes toward improving the mechanical properties of these gels, it also provides pathways for ionic transport to help the gels preserve high conductivity of ILs. The prepared RSF-based gels display a remarkable air stability and reversible loss/absorption water capability in a wide humidity range environment primarily because of the distinguished combination of the IL and water. Therefore, the novel RSF-based gels hold a great potential in various applications as multifunctional, flexible, conductive materials, which are dispensed with encapsulation.
Polyitaconates: A New Family of “All-Polymer” Dielectrics
Sebastian Bonardd - ,
Angel Alegria - ,
Cesar Saldias - ,
Angel Leiva *- , and
Galder Kortaberria *
This work presents the synthesis of new poly(itaconate)s containing sulfone or nitrile pendant groups through conventional radical polymerization together with their characterization and comparison with poly(methacrylate)s containing identical groups. Structural and thermal characterization has been carried out in terms of Fourier transform infrared spectroscopy, differential scanning calorimetry, nuclear magnetic resonance, and thermogravimetric analysis. Characterized by broad band dielectric spectroscopy (BDS), all polymers showed dielectric constant values between 7 and 10 (at 25 °C and 1 kHz) and relative low dielectric loss values (≈0.02). BDS measurements showed, for all the polymers analyzed, notorious subglass transitions even at temperatures below −100 °C, resulting in a broad temperature interval in which these polymers exhibit high dielectric constant and could work without high losses. Therefore, these materials seem to be good candidates for dielectric applications such as energy storage, among others.
Multidimensional Ternary Hybrids with Synergistically Enhanced Electrical Performance for Conductive Nanocomposites and Prosthetic Electronic Skin
Yougen Hu - ,
Xuebin Liu - ,
Lan Tian - ,
Tao Zhao - ,
Hui Wang - ,
Xianwen Liang - ,
Fengrui Zhou - ,
Pengli Zhu *- ,
Guanglin Li - ,
Rong Sun - , and
Ching-Ping Wong
Graphene and silver nanowires (AgNWs) are ideal fillers for conductive polymer composites, but they tend to aggregate in the polymer matrix due to the lack of surface functional groups and large specific surface area, which is hard for the polymer composites filled with them to reach their full potential. Here, ternary hybrids with multidimensional architectures including 3D polystyrene (PS) microspheres, 2D reduced graphene oxide (RGO) nanosheets, and 1D AgNWs are obtained using a simple, but effective, electrostatic attraction strategy. The electrical conductivity (136.25 S m–1) of the ternary hybrid conductive nanocomposites filled with RGO and AgNWs is significantly higher than that of the nanocomposites containing only RGO (3.255 S m–1) at the same total filler loading due to the synergistic effect of RGO and AgNWs. The conductive nanocomposites simultaneously present a low percolation threshold of 0.159 vol % and a maximum electrical conductivity of 1230 S m–1 at 3.226 vol % filler loading. Moreover, a flexible electronic skin based on the multidimensional ternary hybrids is presented, and it exhibits large stretchability, high gauge factor, and excellent cyclic working durability, which is successfully demonstrated in monitoring prosthetic finger motions.
Facile and Versatile Modification of Cotton Fibers for Persistent Antibacterial Activity and Enhanced Hygroscopicity
Qiuquan Cai - ,
Shuliang Yang - ,
Chao Zhang - ,
Zimeng Li - ,
Xiaodong Li *- ,
Zhiquan Shen - , and
Weipu Zhu *
Natural fibers with functionalities have attracted considerable attention. However, developing facile and versatile strategies to modify natural fibers is still a challenge. In this study, cotton fibers, the most widely used natural fibers, were partially oxidized by sodium periodate in aqueous solution, to give oxidized cotton fibers containing multiple aldehyde groups on their surface. Then poly(hexamethylene guanidine) was chemically grafted onto the oxidized cotton fibers forming Schiff bases between the terminal amines of poly(hexamethylene guanidine) and the aldehyde groups of oxidized cotton fibers. Finally, carbon–nitrogen double bonds were reduced by sodium cyanoborohydride, to bound poly(hexamethylene guanidine) covalently to the surface of cotton fibers. These functionalized fibers show strong and persistent antibacterial activity: complete inhibition against Escherichia coli and Staphylococcus aureus was maintained even after 1000 consecutive washing in distilled water. On the other hand, cotton fibers with only physically adsorbed poly(hexamethylene guanidine) lost their antibacterial activity entirely after a few washes. According to Cell Counting Kit-8 assay and hemolytic analysis, toxicity did not significantly increase after chemical modification. Attributing to the hydrophilicity of poly(hexamethylene guanidine) coatings, the modified cotton fibers were also more hygroscopic compared to untreated cotton fibers, which can improve the comfort of the fabrics made of modified cotton fibers. This study provides a facile and versatile strategy to prepare modified polysaccharide natural fibers with durable antibacterial activity, biosecurity, and comfortable touch.
Micropatterning Silver Nanowire Networks on Cellulose Nanopaper for Transparent Paper Electronics
Dabum Kim - ,
Youngsang Ko - ,
Goomin Kwon - ,
Ung-Jin Kim - , and
Jungmok You *
Transparent microelectrodes with high bendability are necessary to develop lightweight, small electronic devices that are highly portable. Here, we report a reliable fabrication method for transparent and highly bendable microelectrodes based on conductive silver nanowires (AgNWs) and 2,2,6,6-tetramethylpiperidine-1-oxy (TEMPO)-oxidized cellulose nanofibers (CNFs). The AgNW-based micropatterns were simply fabricated on glass via poly(ethylene glycol) photolithography and then completely transferred to transparent TEMPO-CNF nanopaper with high bendability via vacuum-assisted microcontact printing (μCP). The AgNW micropatterns were embedded in the surface layer of TEMPO-CNF nanopaper, enabling strong adhesion to the nanopaper substrate. The resulting AgNW micropatterns on the TEMPO-CNF nanopaper showed an optical transparency of 82% at 550 nm and a sheet resistance of 54 Ω/sq when the surface density of AgNWs was as low as 12.9 μg/cm2. They exhibited good adhesion stability and excellent bending durability. After 12 peeling test cycles and 60 s sonication time, the sheet resistance of the AgNW networks embedded on TEMPO-CNF nanopaper increased by only ∼0.12 and ∼0.07 times, respectively. Furthermore, no significant change in electrical resistance was observed even after 3 bending cycles to nearly 90° and 500 cycles of 80% bending strain. Moreover, the AgNW patterns on TEMPO-CNF paper were successfully applied for constructing a transparent electric circuit as well as a solid-state electrochromic device. Overall, we proposed an effective way to fabricate AgNW micropatterns on transparent nanopaper, which can be expanded to various conductive materials for high-performance paper-based electronics.
From Nature to Energy Storage: A Novel Sustainable 3D Cross-Linked Chitosan–PEGGE-Based Gel Polymer Electrolyte with Excellent Lithium-Ion Transport Properties for Lithium Batteries
Dong Xu - ,
Jun Jin - ,
Chunhua Chen - , and
Zhaoyin Wen *
Developing a gel polymer electrolyte with a cross-linked structure is one of the best choices to improve the mechanical strength of the gel polymer electrolyte without sacrificing its lithium-ion transportation properties. However, the cost is always too high. Herein, a novel gel polymer electrolyte based on three-dimensional cross-linked chitosan–poly(ethylene glycol) diglycidyl ether macromolecule network was designed and synthesized through a simple and environmental harmless method, with sustainable and cheap chitosan as major material. The obtained gel polymer electrolyte shows improved mechanical strength of 5.5 MPa, which is higher than that of other gel polymer electrolytes without inert frameworks. The optimized gel polymer electrolyte exhibits a good lithium ionic conductivity of 2.74 × 10–4 S cm–1 with a superior lithium-ion transfer number of 0.869 at 25 °C. Lithium battery assembled with this gel polymer electrolyte demonstrates an initial discharge capacity of 146.8 mA h g–1, which retains 88.49% capacity after 360 cycles at 0.2C. Moreover, this gel polymer electrolyte possesses good interfacial compatibility with lithium anode. Therefore, the growth of lithium dendrite is greatly delayed. This research proves the great possibility of applying sustainable and cost-effective chitosan into gel polymer electrolyte and lithium batteries.
Repeated Intrinsic Self-Healing of Wider Cracks in Polymer via Dynamic Reversible Covalent Bonding Molecularly Combined with a Two-Way Shape Memory Effect
Long Fei Fan - ,
Min Zhi Rong *- ,
Ming Qiu Zhang *- , and
Xu Dong Chen *
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To enable repeated intrinsic self-healing of wider cracks in polymers, a proof-of-concept approach is verified in the present work. It operates through two-way shape memory effect (SME)-aided intrinsic self-healing. Accordingly, a reversible C–ON bond is introduced into the main chain of crosslinked polyurethane (PU) containing an elastomeric dispersed phase (styrene–butadiene–styrene block copolymer, SBS). The PU/SBS blend was developed by the authors recently, and proved to possess an external stress-free two-way SME after programming. As a result, the thermal retractility offered by the SME coupled with the reversible C–ON bonds can be used for successive crack closure and remending based on synchronous fission/radical recombination of C–ON bonds. Moreover, multiwalled carbon nanotubes are incorporated to impart electrical conductivity to the insulating polymer. Repeated autonomic healing of wider cracks is thus achieved through narrowing of cracks followed by chemical rebonding under self-regulating Joule heating. No additional programming is needed after each healing event, which is superior to one-way SME-assisted self-healing. The outcomes set an example of integrating different stimuli-responsivities into single materials.
Surfaces, Interfaces, and Applications
Decomposition of Large Cu Crystals into Ultrasmall Particles Using Chemical Vapor Deposition and Their Application in Selective Propylene Oxidation
Hung-Chi Wu - ,
Ching-Shiun Chen *- ,
Chia-Min Yang - ,
Ming-Chieh Tsai - , and
Jyh-Fu Lee
In this work, we report a novel application of chemical vapor deposition (CVD) in which the calcination and reduction of Cu(thd)2 deposited onto 4.9 wt % Cu/SiO2 induces significant decomposition of 28 nm crystalline Cu into ultrasmall ∼2 nm particles (5.1 wt % Cu/SiO2). The Cu loading slightly increased, but the particle size dramatically decreased. The deposition of Cu(thd)2 onto the Cu surface can initially affect the size reduction of the metallic Cu particles due to charge transfer between Cu(thd)2 and the Cu surface. Thermal treatments, including calcination in air and reduction in H2, can further influence the Cu particle decomposition. The mechanism of change in the Cu particle decomposition was investigated by a variety of experiments, such as X-ray diffraction and in situ X-ray absorption spectroscopy. CVD treatment of Cu/SiO2 can create Cu-rich sites, which effectively enhance the conversion and acrolein yield in selective propylene oxidation. The intermediate associated with propylene oxidation on the Cu catalysts was also examined by IR spectroscopy.
Mechanical Properties and Chemical Reactivity of LixSiOy Thin Films
Yun Xu - ,
Caleb Stetson - ,
Kevin Wood - ,
Eric Sivonxay - ,
Chunsheng Jiang - ,
Glenn Teeter - ,
Svitlana Pylypenko - ,
Sang-Don Han - ,
Kristin A. Persson - ,
Anthony Burrell - , and
Andriy Zakutayev *
Silicon (Si) is a commonly studied candidate material for next-generation anodes in Li-ion batteries. A native oxide SiO2 on Si is often inevitable. However, it is not clear if this layer has a positive or negative effect on the battery performance. This understanding is complicated by the lack of knowledge about the physical properties of the SiO2 lithiation products and by the convolution of chemical and electrochemical effects during the anode lithiation process. In this study, LixSiOy thin films as model materials for lithiated SiO2 were deposited by magnetron sputtering at ambient temperature, with the goal of (1) decoupling chemical reactivity from electrochemical reactivity and (2) evaluating the physical and electrochemical properties of LixSiOy. X-ray photoemission spectroscopy analysis of the deposited thin films demonstrate that a composition close to previous experimental reports of lithiated native SiO2 can be achieved through sputtering. Our density functional theory calculations also confirm that the possible phases formed by lithiating SiO2 are very close to the measured film compositions. Scanning probe microscopy measurements show that the mechanical properties of the film are strongly dependent on lithium concentration, with a ductile behavior at a higher Li content and a brittle behavior at a lower Li content. The chemical reactivity of the thin films was investigated by measuring the AC impedance evolution, suggesting that LixSiOy continuously reacts with the electrolyte, in part because of the high electronic conductivity of the film determined from solid-state impedance measurements. The electrochemical cycling data of the sputter-deposited LixSiOy/Si films also suggest that LixSiOy is not beneficial in stabilizing the Si anode surface during battery operation, despite its favorable mechanical properties.
Multifunctional and Programmable Modulated Interface Reactions on Proteinosomes
Pei Zhou - ,
Shuang Wu - ,
Xiaoman Liu *- ,
Mohammad Hegazy - ,
Guangyu Wu - , and
Xin Huang *
A multiresponsive microcapsule has been synthesized by incorporating photoswitchable spiropyran units and the thermoresponsive monomer N-isopropylacrylamide into membrane lumens. By using functionalized light or thermoresponsive groups, this multifunctional microcapsule can modulate programmed release and interface reactions between lipase and fluorescein diacetate, alkaline phosphatase and fluorescein diphosphate, and others. Exposing this multifunctional microcapsule in a programmed controlled way allowed us to develop schematics to understand complicated interface interactions on protocells.
Using the Surface Features of Plant Matter to Create All-Polymer Pseudocapacitors with High Areal Capacitance
Lushuai Zhang - and
Trisha L. Andrew *
Controlling mesoscale organization in thick films of electroactive polymers is crucial for studying and optimizing charge and ion transport in these disordered materials. Conventional approaches focus on directing long-range polymer aggregation and/or crystallization during film formation by using interfaces, flow and/or shear forces. Here, we describe an alternative method that takes advantage of naturally textured biological substrates and vapor-coating to structure thick-conjugated polymer films. Reactive vapor-coating is a technique that enables in situ synthesis of doped conjugated polymers inside a reduced-pressure reactor. Reactive vapor deposition conformally coats the surface of plant matter, such as leaves and flower petals, with conducting polymer films while leaving these living substrates undamaged. Importantly, the intricate surface features of plant matter are faultlessly reproduced in the coating, effectively creating thick, high-surface-area, electrochemically active conducting polymer electrodes on plant matter. A microstructured, 10 μm thick film of p-doped poly(3,4-ethylenedioxythiophene) on a pilea involucrata leaf acts as an all-polymer pseudocapacitor with a higher areal capacitance (142 mF/cm2) than an analogous film on a planar plastic substrate lacking microstructure (50 mF/cm2). Taken together, reactive vapor deposition and microstructured plant matter present a unique combination of processing technique and substrate than can yield a diverse library of controllably microstructured electronic polymer films.
Highly Sensitive Color Tunablility by Scalable Nanomorphology of a Dielectric Layer in Liquid-Permeable Metal–Insulator–Metal Structure
Eui-Sang Yu - ,
Sin-Hyung Lee - ,
Young-Gyu Bae - ,
Jaebin Choi - ,
Donggeun Lee - ,
Chulki Kim - ,
Taikjin Lee - ,
Seung-Yeol Lee - ,
Sin-Doo Lee *- , and
Yong-Sang Ryu *
A liquid-permeable concept in a metal–insulator–metal (MIM) structure is proposed to achieve highly sensitive color-tuning property through the change of the effective refractive index of the dielectric insulator layer. A semicontinuous top metal film with nanoapertures, adopted as a transreflective layer for MIM resonator, allows to tailor the nanomorphology of a dielectric layer through selective etching of the underneath insulator layer, resulting in nanopillars and hollow voids in the insulator layer. By allowing outer mediums to enter into the hollow voids of the dielectric layer, such liquid-permeable MIM architecture enables to achieve the wavelength shift as large as 323.5 nm/RIU in the visible range, which is the largest wavelength shift reported so far. Our liquid-permeable approaches indeed provide dramatic color tunablility, a real-time sensing scheme, long-term durability, and reproducibility in a simple and scalable manner.
Isotropic Atomic Layer Etching of ZnO Using Acetylacetone and O2 Plasma
A. Mameli - ,
M. A. Verheijen - ,
A. J. M. Mackus - ,
W. M. M. Kessels - , and
F. Roozeboom *
This publication is Open Access under the license indicated. Learn More
Atomic layer etching (ALE) provides Ångström-level control over material removal and holds potential for addressing the challenges in nanomanufacturing faced by conventional etching techniques. Recent research has led to the development of two main classes of ALE: ion-driven plasma processes yielding anisotropic (or directional) etch profiles and thermally driven processes for isotropic material removal. In this work, we extend the possibilities to obtain isotropic etching by introducing a plasma-based ALE process for ZnO which is radical-driven and utilizes acetylacetone (Hacac) and O2 plasma as reactants. In situ spectroscopic ellipsometry measurements indicate self-limiting half-reactions with etch rates ranging from 0.5 to 1.3 Å/cycle at temperatures between 100 and 250 °C. The ALE process was demonstrated on planar and three-dimensional substrates consisting of a regular array of semiconductor nanowires (NWs) conformally covered using atomic layer deposition of ZnO. Transmission electron microscopy studies conducted on the ZnO-covered NWs before and after ALE proved the isotropic nature and the damage-free characteristics of the process. In situ infrared spectroscopy measurements were used to elucidate the self-limiting nature of the ALE half-reactions and the reaction mechanism. During the Hacac etching reaction that is assumed to produce Zn(acac)2, carbonaceous species adsorbed on the ZnO surface are suggested as the cause of the self-limiting behavior. The subsequent O2 plasma step resets the surface for the next ALE cycle. High etch selectivities (∼80:1) over SiO2 and HfO2 were demonstrated. Preliminary results indicate that the etching process can be extended to other oxides such as Al2O3.
Electrodeposited Epitaxial Cu(100) on Si(100) and Lift-Off of Single Crystal-like Cu(100) Foils
Caleb M. Hull - and
Jay A. Switzer *
A two-step potential electrodeposition technique is described which gives epitaxial films of Cu(100) on n-Si(100). Nucleation of epitaxial seeds occurs at −1.5 VAg/AgCl, whereas the film is grown at −0.5 VAg/AgCl. Cu deposition occurs with a Faradaic efficiency of 82.0% as determined spectrophotometrically. Epitaxy is achieved through a 45° in-plane rotation of Cu with respect to Si, which is shown by X-ray analysis. The 45° rotation reduces the lattice mismatch from −33.43% for an unrotated film to −5.86% for a 45° rotated film. Mosaicity, as determined via X-ray rocking curves, decreases with increasing thickness, going from a full width at half maximum of 3.99° for a 30 nm thick film to 1.67° for a 160 nm thick film. This translates to an increasing quality of epitaxy with increasing thickness. High resolution transmission electron microscopy imaging shows an amorphous SiOx interlayer between Cu and Si. Etching of SiOx with 5% HF allows epitaxial lift-off of the copper film, giving single crystal-like Cu(100) foils. Cu(100) films and single crystal-like foils have potential to be used as catalysts for CO2 reduction, substrates for technologically important materials like spintronic multilayer magnetic stacks and high temperature superconductors, and as active surfaces toward galvanic replacement by platinum group elements. Additionally, the foils could be used as single crystal-like substrates for flexible electronics.
Long-Term Stable Transferred Organic Photoactive Layer-Based Photodiode with Controlled Wetting through Interface Stabilization
Woongsik Jang - and
Dong Hwan Wang *
The stamping transfer process, which provides a precise patterning of the target material without the limitation of an underlying layer, has attracted significant attention for large-scale roll-to-roll fabrication. Despite the need to minimize the peeling energy, expressed as the sum of adhesion energies, for a simple transfer process, many studies have not considered this effect. In this study, we introduced a wetting coefficient related with adhesions between polymers for the transfer design of organic photosensitive materials. We observed a difference in adhesion between polymer blends depending on the surface energy of the mold. We designed high-surface-energy polyurethane acrylate to enable a residue-free transfer process. The transfer process significantly contributed to the device stability through changes in dark currents, photocurrents, responsivity, and detectivity over time, compared to spin coating. In particular, the detectivity was maintained over 95% after 360 h, and no burn-in loss of internal resistance was observed in the device with a transferred active layer. X-ray photoelectron spectroscopy showed that a large interfacial change between poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl):[6,6] phenyl C71 butyric acid methyl ester obtained through spin coating occurred owing to solution penetration, whereas the transfer process provided a constant interface owing to morphology stabilization. Therefore, the transfer process with optimized adhesion properties can improve the device operation durability without burn-in loss, enabling a cost-effective fabrication of organic optoelectronic devices.
Vapor-Phase Cleaning and Corrosion Inhibition of Copper Films by Ethanol and Heterocyclic Amines
Luis Fabián Peña *- ,
Jean-Francois Veyan - ,
Michael A. Todd - ,
Agnes Derecskei-Kovacs - , and
Yves J. Chabal
Cleaning and passivation of metal surfaces are necessary steps for selective film deposition processes that are attractive for some microelectronic applications (e.g., fully aligned vias or self-aligned contacts). For copper, there is limited knowledge about the mechanisms of the copper oxide reduction process and subsequent passivation layer formation reactions. We have investigated the in situ cleaning (i.e., oxidation and reduction by vapor-phase species) and passivation of chemical–mechanical polishing (CMP)-prepared Cu films in an effort to derive the mechanisms associated with selectively tailoring the surface chemistry. By monitoring the interaction of vapor-phase ethanol with the surface species generated after ozone cleaning at 300 °C, we find that the optimum procedure to remove these species and avoid byproduct redeposition is to use atomic layer deposition (ALD)-like binary cycles of ethanol and N2, with active pumping. We have further explored passivation of clean Cu using benzotriazole and 2,2′-bipyridine in an ALD environment. Both molecules chemisorb on clean Cu in an upright orientation, with respect to the metal surface at temperatures higher than the melting point of the organic inhibitors (100 ≤ T < 300 °C). Both molecules desorb without decomposition from clean Cu above 300 °C but not from Cu2O. Previous studies related to the passivation of Cu surfaces using heterocyclic amines have focused on solution-based or ultrahigh vacuum applications of the passivation molecules onto single crystalline Cu samples. The present work explores more industrially relevant vapor-phase passivation of CMP-cleaned, electroplated Cu samples using ALD-like processing conditions and in situ vapor-phase cleaning.
Gated Single-Molecule Transport in Double-Barreled Nanopores
Liang Xue - ,
Paolo Cadinu - ,
Binoy Paulose Nadappuram - ,
Minkyung Kang - ,
Ye Ma - ,
Yuri Korchev - ,
Aleksandar P. Ivanov *- , and
Joshua B. Edel *
This publication is Open Access under the license indicated. Learn More
Single-molecule methods have been rapidly developing with the appealing prospect of transforming conventional ensemble-averaged analytical techniques. However, challenges remain especially in improving detection sensitivity and controlling molecular transport. In this article, we present a direct method for the fabrication of analytical sensors that combine the advantages of nanopores and field-effect transistors for simultaneous label-free single-molecule detection and manipulation. We show that these hybrid sensors have perfectly aligned nanopores and field-effect transistor components making it possible to detect molecular events with up to near 100% synchronization. Furthermore, we show that the transport across the nanopore can be voltage-gated to switch on/off translocations in real time. Finally, surface functionalization of the gate electrode can also be used to fine tune transport properties enabling more active control over the translocation velocity and capture rates.
Fifteen Nanometer Resolved Patterns in Selective Area Atomic Layer Deposition—Defectivity Reduction by Monolayer Design
Rudy Wojtecki *- ,
Magi Mettry - ,
Noah F. Fine Nathel - ,
Alexander Friz - ,
Anuja De Silva - ,
Noel Arellano - , and
Hosadurga Shobha
Selective area atomic layer deposition (SA-ALD) offers the potential to replace a lithography step and provide a significant advantage to mitigate pattern errors and relax design rules in semiconductor fabrication. One class of materials that shows promise to enable this selective deposition process are self-assembled monolayers (SAMs). In an effort to more completely understand the ability of these materials to function as barriers for ALD processes and their failure mechanism, a series of SAM derivatives were synthesized and their structure—property relationship explored. These materials incorporate different side group functionalities and were evaluated in the deposition of a sacrificial etch mask. Monolayers with weak supramolecular interactions between components (for example, van der Waals) were found to direct a selective deposition, though they exhibit significant defectivity at and below 100 nm feature sizes. The incorporation of stronger noncovalent supramolecular interacting groups in the monolayer design, such as hydrogen bonding units or pi–pi interactions, did not produce an added benefit over the weaker interacting components. Incorporation of reactive moieties in the monolayer component that enabled the polymerization of an SAM surface, however, provided a more effective barrier, greatly reducing the number and types of defects observed in the selectively deposited ALD film. These reactive monolayers enabled the selective deposition of a film with critical dimensions as low as 15 nm. It was also found that the selectively deposited film functioned as an effective barrier for isotropic etch chemistries, allowing the selective removal of a metal without affecting the surrounding surface. This work enables selective area ALD as a technology through (1) the development of a material that dramatically reduces defectivity and (2) the demonstrated use of the selectively deposited film as an etch mask and its subsequent removal under mild conditions.
Unusual Moisture-Enhanced CO2 Capture within Microporous PCN-250 Frameworks
Yongwei Chen - ,
Zhiwei Qiao - ,
Jiali Huang - ,
Houxiao Wu - ,
Jing Xiao - ,
Qibin Xia *- ,
Hongxia Xi - ,
Jun Hu - ,
Jian Zhou *- , and
Zhong Li
Developing metal–organic frameworks (MOFs) with moisture-resistant feature or moisture-enhanced adsorption is challenging for the practical CO2 capture under humid conditions. In this work, under humid conditions, the CO2 adsorption behaviors of two iron-based MOF materials, PCN-250(Fe3) and PCN-250(Fe2Co), were investigated. An interesting phenomenon is observed that the two materials demonstrate an unusual moisture-enhanced adsorption of CO2. For PCN-250 frameworks, H2O molecule induces a remarkable increase in the CO2 uptake for the dynamic CO2 capture from CO2/N2 (15:85) mixture. For PCN-250(Fe3), its CO2 adsorption capacity increases by 54.2% under the 50% RH humid condition, compared with that under dry conditions (from 1.18 to 1.82 mmol/g). Similarly, the CO2 adsorption uptake of PCN-250(Fe2Co) increases from 1.32 to 2.23 mmol/g, exhibiting a 68.9% increase. Even up to 90% RH, for PCN-250(Fe3) and PCN-250(Fe2Co), obvious increases of 43.7 and 70.2% in the CO2 adsorption capacities are observed in comparison with those under dry conditions, respectively. Molecular simulations indicate that the hydroxo functional groups (μ3-O) within the framework play a crucial role in improving CO2 uptake in the presence of water vapor. Besides, partial substitution of Fe3+ by Co2+ ions in the PCN-250 framework gives rise to a great improvement in CO2 adsorption capacity and selectivity. The excellent moisture stability (stable even after exposure to 90% RH humid air for 30 days), superior recyclability, as well as moisture-enhanced feature make PCN-250 as an excellent MOF adsorbent for CO2 capture under humid conditions. This study provides a new paradigm that PCN-250 frameworks can not only be moisture resistant but can also subtly convert the common negative effect of moisture to a positive impact on improving CO2 capture performance.
Application of Antibody-Powered Triplex-DNA Nanomachine to Electrochemiluminescence Biosensor for the Detection of Anti-Digoxigenin with Improved Sensitivity Versus Cycling Strand Displacement Reaction
Shan-Shan Yang - ,
Ming-Hui Jiang - ,
Ya-Qin Chai - ,
Ruo Yuan *- , and
Ying Zhuo *
The accurate and rapid quantitative detection of antibodies had a significant influence in controlling and preventing disease or toxin outbreaks. In this work, we first introduce the antibody-powered triplex-DNA nanomachine to release cargo DNA as a substitute target for sensitive electrochemiluminescence (ECL) detection of anti-digoxigenin based on a novel ternary ECL system. It is worth noting that the cargo DNA as a substitute target of antibody can further participate in an enzyme-assisted cycling strand displacement reaction to achieve ECL signal amplification and improve the sensitivity of antibody detection. Additionally, porous palladium nanospheres with a considerable catalytic activity were first applied as a coreaction accelerator to efficiently enhance the intensity of the ECL system of rubrene microblocks as luminophore and dissolved O2 as an endogenous coreactant. With the resultant ternary ECL system as a biosensing platform, a significantly enhanced initial signal was achieved in advance. Then, the ferrocene-labeled quenching probes were employed to reduce initial signal and obtain the low-background signal. Eventually, the cargo DNA made the quenching probes release and recover the signal in the presence of anti-digoxigenin. Thereupon, the wide linear range (0.01–200 nM) and low limit of detection (6.7 pM) were obtained, and this method not only reduces conjugation steps but also provides a sensitive and novel ECL analysis platform for the trace detection of other antibodies and antigen.
Additions and Corrections
Correction to Substrate-Independent Micropatterning of Polymer Brushes Based on Photolytic Deactivation of Chemical Vapor Deposition Based Surface-Initiated Atom-Transfer Radical Polymerization Initiator Films
Ramya Kumar - ,
Alexander Welle - ,
Fabian Becker - ,
Irina Kopyeva - , and
Joerg Lahann *
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