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Design of a Compact Multicyclic High-Performance Atmospheric Water Harvester for Arid Environments
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  • Xiangyu Li*
    Xiangyu Li
    Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
    Department of Mechanical Aerospace and Biomedical Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States
    *Email: [email protected];.
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    Orcidhttps://orcid.org/0000-0003-0116-7307
  • Bachir El Fil*
    Bachir El Fil
    Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
    *Email: [email protected]
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  • Buxuan Li
    Buxuan Li
    Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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  • Gustav Graeber
    Gustav Graeber
    Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
    Department of Chemistry, Humboldt-Universität zu Berlin, 12489 Berlin, Germany
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    Orcidhttps://orcid.org/0000-0003-0658-6084
  • Adela C. Li
    Adela C. Li
    Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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  • Yang Zhong
    Yang Zhong
    Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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    Orcidhttps://orcid.org/0000-0001-6748-903X
  • Mohammed Alshrah
    Mohammed Alshrah
    Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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  • Chad T. Wilson
    Chad T. Wilson
    Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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  • Emily Lin
    Emily Lin
    Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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ACS Energy Letters

Cite this: ACS Energy Lett. 2024, 9, 7, 3391–3399
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https://doi.org/10.1021/acsenergylett.4c01061
Published June 26, 2024

Copyright © 2024 The Authors. Published by American Chemical Society. This publication is licensed under

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Abstract

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Water scarcity remains a grand challenge across the globe. Sorption-based atmospheric water harvesting (SAWH) is an emerging and promising solution for water scarcity, especially in arid and noncoastal regions. Traditional approaches to AWH such as fog harvesting and dewing are often not applicable in an arid environment (<30% relative humidity (RH)), whereas SAWH has demonstrated great potential to provide fresh water under a wide range of climate conditions. Despite advances in materials development, most demonstrated SAWH devices still lack sufficient water production. In this work, we focus on the adsorption bed design to achieve high water production, multicyclic operation, and a compact form factor (high material loading per heat source contact area). The modeling efforts and experimental validation illustrate an optimized design space with a fin-array adsorption bed enabled by high-density waste heat, which promises 5.826 Lwater kgsorbent–1 day–1 at 30% RH within a compact 1 L adsorbent bed and commercial adsorbent materials.

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About two-thirds of the global population is suffering from water scarcity, and it is estimated that about 40% of the global annual water demand will not be met by 2030, posing further challenges to public health, agriculture, and industrial applications. (1,2) While desalination is a maturing technology that shows potential to produce large amounts of fresh water in coastal regions, large-scale desalination based on reverse osmosis demands large capital investment, produces a significant amount of brine waste, and requires sufficient seawater supply, while only being viable in developed coastal regions. (3) However, there is about 1300 trillion liters of fresh water in the atmosphere that could be readily harvested without relying on the existing liquid water supply. (4) Sorption-based atmospheric water harvesting (SAWH) (5−13) promises potable water production in extreme arid environments where conventional atmospheric water harvesting solutions such as fog harvesting and dewing are infeasible. Most of the existing SAWH prototypes in literature are solar-driven water harvesting devices (Figure 1A) incorporating the development of novel adsorbent materials, (7,14−17) including zeolites, (8) metal–organic framework materials (MOFs), (5,6) and hygroscopic composite. (9,10) Kim et al. (5,6) demonstrated a solar-driven SAWH with a 1 mm thick MOF-801 coating operated at a relative humidity (RH) of 20%. Further optimization of such devices (11) and the adoption of dual stages (8) helped recycle the latent heat of condensation to increase the performance of SAWH devices. However, due to the low solar energy density and inconsistent weather conditions, the amount of water harvested from existing prototypes is still inadequate to meet the daily human needs. (18−24) Shan et al. (9) have developed a modularized water harvester with scalable, low-cost, and lightweight LiCl impregnated hygroscopic composite (Li-SHC) sorbents. This allows one to increase the productivity of the system through undergoing desorption of several batches. As an alternative to solar energy as the desorption energy source, electricity, produced by photovoltaic panels, counts as one of the higher energy sources for SAWH devices (Figure 1B). This enables multicyclic operations and maximizes the amount of water collection. (7) However, this comes at a substantial energy cost with the multicyclic desorption process due to the large adsorption enthalpy, also known as desorption enthalpy. Comparably, existing waste heat from various sources can offer low-cost, high-density energy. The performance of current state-of-the-art solar (passive) and active devices is shown in Table 1. Overall, it is critical to leverage high-density waste heat and develop a compact and cost-effective high-performance SAWH device that meets the growing demand for potable water in extreme arid environments.
Table 1. Performance Summary of Solar-Driven and High Energy Density-Driven SAWH (25)
 Conventional Passive SAWH (5,6,8,17)Active (High Energy Density) SAWH (7,9,10,20,22,26)
Desorption Energy SourceSolarCombustion, Electricity, Waste Heat
Daily CyclesSingleMultiple
Desorption Temperature70–100 °C>100–150 °C
Water Collection per kg of Sorbent0.1–0.25 L/day0.57–2.8 L/day
Daily Water Harvested0.75–60 mL20–370 mL
Specific Energy Consumptiona4.65–6.88 kWh/L11.15–22.81 kWh/L
a

The specific energy consumption (SEC) is calculated based on kWhth (thermal) per liters of water collected daily.

Figure 1

Figure 1. Comparison between solar-driven (passive) and high-energy-driven SAWH devices. (A) SAWH designs driven by solar energy. Limited by solar energy density, the adsorption/desorption cycle often synchronizes with the day–night cycle, resulting in a small amount of daily water production. (B) High-density energy sources to drive SAWH include electricity, biomass combustion, or various sources of waste heat. With high-density energy to drive desorption, multicyclic operation with thinner coatings achieves faster kinetics and higher daily water production.

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In this work, we design a compact adsorption bed for an atmospheric water harvesting device driven by high-density waste heat, therefore enabling fast cycling kinetics and maximizing the daily water production. To design a fast-cycling device, it is important to consider both material and device design, which helps in optimizing the multicyclic performance of the device. Material-level water sorption properties, including sorption isotherm, water diffusivity, and adsorption enthalpy hads, are the heart of SAWH devices. An ideal sorbent should exhibit a high-water uptake with negligible hysteresis and fast water sorption kinetics and require a minimal amount of energy to regenerate. All of these are essential to design the device where the sorbent will be incorporated. Additionally, material innovations can only be effective when the insights from material science can be organically connected to device realization, although there is still a giant knowledge barrier between them. Device operation is determined by the water transport and energy exchange processes that need to be optimized synergistically by incorporating materials insights. By utilizing an array of thin adsorption fins (∼mm) rather than a single-layer thick coating (∼cm), rapid adsorption cycling is enabled. We identify and optimize several key design parameters associated with air channels between the adsorbent fins to maximize water uptake. Specifically, there is a trade-off between water vapor supply and diffusion resistance for multicycle operation. A thermofluidic numerical model was developed to optimize the novel adsorption bed. With enhanced adsorption kinetics and high-density desorption energy, the proposed design promises high water production within a compact form factor. To validate the numerical model, an experimental prototype of the adsorption bed is fabricated and coated with a commercial adsorbent. We used AQSOA-FAM-Z02 as the adsorbent in all of the experiments due to its low cost and wide availability; however, the work can be readily translated to other adsorbents. AQSOA-FAM-Z02 is based on the (silico)aluminophosphate SAPO-34 zeolite, hereafter referred to as AQSOA-Z02. The prototype (6 cm × 6 cm × 5.5 cm) is used to characterize adsorption and desorption processes, with a volume of 200 mL and total mass of 0.4 kg incorporating 10.85 g of Z02. Both modeling and experimental efforts show that a fin-array adsorbent bed with a compact 1 L form factor promises 1.3 L day–1 potable water at 30% RH, while utilizing 230 g AQSOA Z02. Overall, this work provides a design framework for a compact adsorbent bed for an SAWH device driven by a waste heat energy source.

Adsorption Bed Design and Modeling

State-of-the-art solar-driven SAWH uses a flat adsorbent coating for water adsorption, as depicted in Figure 1A,B. Previous studies often adopted thick adsorption coatings to ensure sufficient and compact sorbent loading while operating a single cycle per day, synchronized with the day–night cycle. (5,8) The thickness of the coating was determined to optimize the usage of daytime solar energy for desorption processes while harnessing the cooler and higher humidity nighttime conditions for effective adsorption, thus aligning operation with the natural diurnal thermal cycles. This strategy leads to long cycle times and slow kinetics, resulting in a small amount of daily water production, as illustrated in Figure 1A. Recent studies (7,9,27) explored multicyclic operation (Figure 1B), which utilized thinner coatings for faster kinetics, as well as dual-stage configuration for latent heat recovery to achieve higher energy efficiency. (8,28,29) Although various device designs have been investigated, overall water production is still significantly limited by passive desorption using solar energy, and the slow kinetics of the adsorbent bed hinders multicyclic operation. With flat single-layer adsorbent coatings fabricated with a dip coating approach, an intrinsic trade-off exists between the cycling kinetics and device compactness, as shown in Figure 2A. The sorbent coating kinetics scale as Dv /δads2, where Dv is the effective diffusivity of vapor transport through the coating thickness δads. On the other hand, compactness is quantified as mads/Abase, where mads and Abase are the adsorbent mass and base projected areas of the adsorbent coating. Alternatively, to maintain both favorable kinetics and compactness (blue region in Figure 2A), we propose a fin-array adsorbent bed (Figure 2B). The fin array (aligned in the x-axis) enables faster kinetics due to a thin coating while maintaining a compact form factor. Each adsorbent fin consists of a metal sheet sandwiched between two metal foams. The metal fin enables efficient heat transfer, while the metal foams are coated with sorbent. The fins are aligned in parallel with narrow air gaps in between. Humid air flows along the y-axis during the adsorption process. Figure 2C is the front view of the adsorption bed. The blue arrows represent vapor diffusion and adsorption from the humid air flow to the adsorbent coatings, and dashed blue arrows represent desorbed water vapor from the heated adsorbent coating. Due to the thin coatings (∼mm) that are exposed to humid air flow, the enhanced kinetics for adsorption process promise rapid cycling operations. Additionally, by minimizing the air gap thickness between the adsorbent fins, we ensured that a large amount of adsorbent can be packed within a small footprint. Thin air gaps also enhance convective heat transfer, which effectively prevents the overheating of adsorbent coatings. Once the adsorption cycle is completed, the fin base is heated by waste heat for desorption. Thermal energy diffuses from the base along the height of the fins (z-axis), leading to a temperature rise and releasing the adsorbed water vapor.

Figure 2

Figure 2. Adsorbent bed design considerations. (A) Optimization of kinetics and compactness for atmospheric water harvesting with single-layer coatings. Humid air flows above the coating surface. Thin coatings enable fast kinetics and multicyclic operation but sacrifice the compactness. (B) Compact adsorbent bed design with an array of adsorbent fins (arranged in the x-axis), consisting of metal sheets and adsorbent coatings. Humid air flows through the air gaps (along the y-axis) between the adsorbent fins. (C) Front view during the adsorption and desorption processes. During adsorption, humid air enters the air channels and water vapor is adsorbed into the coating, illustrated by blue arrows. During desorption, the sorbent coating is heated by thermal energy input from the base along the z-axis. Desorbed water vapor is represented by dashed blue arrows.

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During the adsorption process, the mass transport of water vapor from the humid air flows to the adsorbent crystals consisting of three main resistance, Rair, Rcoating, and Rcrystal, as shown in Figure 3A. The advective transport resistance is neglected due to the high Peclet number with the humid air flow, summarized in Supporting Information Table S1. The vapor transfer from humid air flow to the coating surface is governed by mass diffusion (Rair), determined by the vapor diffusivity and air gap thickness. Within the porous coatings, mass transport is dominated by intercrystalline diffusion (Rcoating). Lastly, both particle size and intracrystalline diffusivity affect the transport resistance (Rcrystal) into the adsorbent crystals from the adsorbent coating pores. Figure 3B illustrates the effect of air flow velocities on the average water uptake during adsorption. Here, we assumed a simplified Type IV isotherm profile, with a step function at 6% RH. More details on adsorption simulations are included in Note S1 and Figures S1 and S2. Enabled by a higher flow rate, a larger amount of moisture is supplied to the adsorbent, leading to faster overall kinetics, with the trade-off of a higher pressure drop. Figure 3C shows the outlet relative humidity at different air flow velocities and air gaps after a 30 min adsorption cycle. The vapor supply can restrain the adsorption rate, leading to lower outlet humidity at low air flow velocities or small air gaps, as shown in Figure 3D. With an arid ambient condition (RH = 10%), there is a minimal air gap needed to ensure sufficient vapor supply based on air flow velocities. However, as the air gap continues to increase, the adsorption rate drops, resulting in an optimized air gap where a maximized adsorption rate is achieved. An air gap too large will reduce the water vapor diffusion rate to the coating surface since the vapor transport rate perpendicular to the air flow is inversed proportional to dair2. A scaling analysis is provided in Note S2 and Figure S5. Therefore, a larger air gap benefits the vapor supply but has a negative impact on Rair and the vapor transport rate. This shows that there exists an optimal air gap thickness, which is a critical design parameter to maximize the adsorption potential of the materials. This is contrary to traditional thoughts that larger air gaps are preferred with a greater vapor supply.

Figure 3

Figure 3. Adsorption simulation results. (A) Water vapor transport path and associated mass transport resistance. (B) Transient water uptake of adsorbent with different air flow velocities. (C) Outlet air flow humidity with different air gap thicknesses and air velocities. (D) Water uptake as a function of different air velocities and air gap thicknesses. Optimized air gaps are identified, as a trade-off between vapor supply and diffusion resistance in the air channels.

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Figure 4 illustrates the desorption simulation with a constant temperature of 90 °C to simulate the high-density waste heat (see Figures S3 and S4 for more information). Panels A and B of Figure 4 show the temperature and water uptake profiles at 300 s. Due to the high adsorption enthalpy (∼3420 kJ kg–1 for AQSOA Z02) (30) and high thermal conductivity of the adsorbent fin, there is minor temperature variation in the adsorbent fin. The desorption initiates at the fin base and continues toward the fin tip, as thermal energy travels along the fin height. The transient temperature and water uptake responses are shown in Figure 4C. Gray dashed lines highlight three main phases. From the start up to 50 s, thermal diffusion dominates before the adsorbent reaches its desorption temperature. From 50 to 700 s, the applied thermal energy desorbs the water vapor out from the adsorbent. Once desorption is close to completion at around 700 s, the thermal energy starts to contribute to the sensible heating, which leads to adsorbent saturation to the base temperature. In this design, desorption occurs within a closed system, i.e., the sorbent bed is isolated from the ambient air, to ensure that the desorbed water vapor is contained in the system to maximize the amount of water condensate. More detailed adsorbent bed optimization is shown in Note S3 and Figures S6–S8.

Figure 4

Figure 4. Desorption simulation results. (A) Temperature profile and (B) adsorbent water uptake profile at 300 s after the start of desorption. (C) Temperature and water uptake response during the desorption operation. Red and green curves represent the average temperatures of adsorbent and condenser, and the blue dashed curve represents water uptake in the adsorbent. In the first 50 s, thermal energy diffuses through the fins, before the adsorbent reaches its desorption temperature. As the temperature increases, water vapor is desorbed, increasing the condenser temperature and reducing the water uptake. Due to the constant heat flux, the desorption rate is mostly linear, until the adsorbent is further heated at the end of desorption.

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Adsorption and Desorption Experimental Testing

In this study, we conceived a proof-of-concept experimental setup with the aim of comprehensively characterizing both the adsorption and desorption processes. Specifically, we devised two smaller-scale experimental configurations (Figure 5A,B), to experimentally validate the numerical thermofluidic models developed for the analysis of adsorption and desorption phenomena, respectively. Within each of the experimental setups, we assembled fin structures on a copper base plate. Each fin unit consisted of a copper sheet with a thickness of 0.15 mm, sandwiched between two layers of copper foams (coating thickness, δads, of 0.6 mm and a porosity, ε ≥ 0.98). The adsorbent fins had a length (L) of 35 mm and a width (W) of 40 mm, with a 2 mm air gap separating them.

Figure 5

Figure 5. Experimental validation of adsorption and desorption for AQSOA Z02 adsorption bed. (A) Experimental validation setup of adsorption process, where water adsorption is monitored with weight. (B) Experimental validation setup of the desorption process in an enclosed system, where heat is provided with cartridge heaters. Experimental results are compared with numerical models for (C) adsorption and (D) desorption processes. Experimental and modeling adsorption data are represented by blue solid line and black dashed line, respectively.

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In the context of the adsorption setup, as elucidated in Figure 5A, an acrylic enclosure was used to guide the fan air intake throughout the adsorption bed. The entire assembly was placed on top of a high-precision mass balance, facilitating quantification of the mass of water vapor adsorbed from the surrounding atmosphere as a function of time. On the other hand, the desorption setup, as shown in Figure 5B, has three cartridge heaters, each with a maximum power capacity of 60 W and J-Type thermocouples attached. The temperature of the copper block was controlled through a proportional-integral derivative (PID) temperature controller. During desorption, an aluminum enclosure was used to contain the adsorption bed. To minimize the dissipation of thermal energy, the aluminum enclosure was insulated. Three J-Type thermocouples were positioned at the base, mid-point, and tip of an adsorbent fin, respectively, thereby measuring a comprehensive temperature profile across the entire fin length. To reduce heat transport from the copper base to the condenser and to prevent any vapor leakage from the experimental apparatus, a high-temperature silicon gasket was placed between the aluminum enclosure and the condenser. Furthermore, the condenser temperature was measured throughout the desorption experiment. The resulting condensate was collected within a graduated cylinder and placed on a mass balance. This configuration facilitated continuous quantification of the mass of accrued water over time.
The experimental setups are illustrated in Figure 5A,B, where the temperature, humidity, and mass data were collected. Detailed information on the experimental setup is included in Note S4 and Figures S9–S11. Numerical simulations were also conducted based on the adsorbent isotherm of Z02 and kinetics. Both experimental characterization and numerical simulation agree well to demonstrate the rapid kinetics, which enables saturated adsorption within 30 min, as shown in Figure 5C, contributed by the fin-array adsorbent bed design. A nominalized weight is defined as actual water adsorbed over the saturated water uptake based on material isotherms. Given available waste heat from biomass combustion or transportation vehicles, the desorption process can be significantly reduced to less than 10 min (Figure 5D) due to its high energy density. Solid lines represent experimental temperature characterization and collected water mass, and dashed lines are simulated from numerical models. The deviation of fin temperatures is due to the possible heat loss of the system, with more analysis in Note S4. A delay was observed between the vapor generation from modeling and liquid water collection from experiment due to the time delay of condensed water flowing to the collecting vessel, which also contributed to the slight offset in the condenser temperature. Based on the modeling and experimental results, the proposed adsorption bed design promises more than 24 cycles per day of water adsorption with high-density waste heat. This translates to ∼1.3 L potable water per day with 0.23 kg of zeolite AQSOA Z02 and a 1 L adsorbent bed, or 2–5 times the daily water production compared to that of previous devices. (25,31)
This proposed compact adsorption bed design provides a reliable and effective source of potable water production that can be integrated into various existing applications, such as in buildings, industrial plants, and transportation with suitable high-density waste heat. Further development and implementation of other novel materials can benefit and improve upon the above performance, including metal–organic frameworks and salt-impregnated hybrid materials that achieve higher water uptake and more accessible desorption temperature. (15) Water vapor transport inside packed sorbent coatings directly influences the kinetics of water capture and release. Generally, the sorption kinetics are governed by multistep water transport processes, including interface resistance (Rair), diffusion resistance in the coating, i.e., intercrystalline resistance through the coating (Rcoating), and diffusion within the crystal, i.e., intracrystalline resistance (Rcrystal) as depicted in Figure 3A. Typically, significant decline in sorption and desorption kinetics could be a bottleneck for all kinds of large-scale packed sorbents, which mainly tends to increase the diffusion resistances of water vapor transport within the coating, Rcoating. To overcome this challenge, we designed a fin-based sorbent bed (Figure 6A) that maintains favorable kinetics while providing a similar water uptake capacity of the sorbent bed. Two fundamental key properties dictate the sorbent’s performance: (1) equilibrium water uptake (weq) and (2) kinetics given by the ratio of intracrystalline diffusivity to the square of the particle radius (Dμ/R2). The ideal sorbent for a multicycle atmospheric water harvesting device would have high uptake and fast kinetics, i.e., maximizing the product of the latter two factors (weq·Dμ/R2). However, as the thickness of the sorbent layer increases, the effect of Rcoating (τδadsεDv,air) becomes more pronounced, where δads is the thickness of the sorbent layer, ε is the coating packing porosity, τ is tortuosity estimated by random packing porosity ∼ε –1/2, and Dv,air is the vapor diffusivity in air (∼2.6 × 10–5 m2 s–1). (32) Figure 6B shows the heat map of the instantaneous amount of water uptake after a one-time constant (∼63.2% of the steady state uptake) as a function of intrinsic sorbent properties, i.e., weq Dμ/R2(y-axis) and intercrystalline mass transfer time scale (δads2ε3/2Dv,air) on the x-axis. Figure 6B clearly illustrates the importance of the sorbent coating, especially in regions where the product of equilibrium uptake and kinetics is less than 2 × 10–4 s–1. As the coating thickness increases, instantaneous water uptake into the coating layer decreases. It highlights the significance of the intercrystalline mass transfer resistance and its effect on water capacity. Typically, the ability to tune the sorbent could be difficult and limited; however, significant performance improvement exists just by optimizing the design of the adsorbent bed. As described earlier, enhancing the coating performance could be achieved either through its packing porosity or via the optimization of the vapor channel tortuosity. El Fil et al. (33) have shown a 1.7× enhancement in sorption kinetics by creating vapor channels, thereby reducing tortuosity. In this work, we focus on coating thickness and overall water capacity to achieve higher amounts of daily water collection. Therefore, the key research point for lowering the diffusion resistance in coatings is to primarily optimize the diffusion thickness, which is directly affected by both the coating thickness and the tortuosity factor.

Figure 6

Figure 6. Water sorption and kinetics in the fin-structured adsorbent bed. (A) Schematic showing humid air flowing through the air gap between adsorbent coatings. (B) Design map showing the water uptake as a function of the product of equilibrium water uptake of the adsorbent and its kinetics, weqDμ/R2, and the time scale of mass transfer in the sorbent coating (δads2ε3/2Dv). (C) Water uptake as a function of time as a function of equilibrium uptake, intracrystalline diffusivity, and coating thickness. (D) Cumulative amount of daily water collection for different sorbent characteristics and thicknesses.

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Figure 6C shows the instantaneous water uptake as a function of time. It highlights the effect of equilibrium uptake (weq = 0.25 and 1.00 gwater gsorbent–1), intracrystalline diffusivity (Dμ = 10–17and 10–16 m2 s–1), and coating thickness (δads = 0.6 and 2 mm). At low uptakes (0.25 gwater gsorbent–1) and low kinetics (10–17 m2 s–1), the effect of the coating thickness is not significant. However, at higher uptake and kinetics (1.00 gwater gsorbent–1 and 10–16 m2 s–1), the coating thickness becomes the dominant factor. It is important to note that a random porous medium was assumed with a packing porosity of 0.5. With thicker coatings, less water can be adsorbed due to diffusion-limited vapor transfer through the coating thickness, as depicted by the regime map (Figure 6B). This favorable sorption performance reflects favorably on the total amount of daily water collected as shown in Figure 6D. For the same total amount of sorbent, the amount of water collected could increase by 1 order of magnitude due to the choice of sorbent and the sorbent bed geometry. For a sorbent with low equilibrium uptake of 0.25 gwater gsorbent–1 and intracrystalline diffusivity of 10–17 m2 s–1, the total amount of water collected for a sorbent layer of 0.6 and 2 mm is 133 and 71 mL, respectively. On the other hand, at higher uptakes and fast kinetics (1.00 gwater gsorbent–1 and 10–16 m2 s–1), the total amount of water collected for sorbent layers of 0.6 and 2 mm is 1340 and 396 mL, respectively.
In conclusion, a fin-array adsorbent bed design was proposed, offering rapid kinetics with high-density waste heat, enabled by a fin-array adsorbent bed design and millimeter thick adsorbent coatings for a compact form factor. The air gap between adsorbent fins was identified as a key design parameter to maximize water adsorption, optimized to ensure sufficient water vapor supply, and minimize mass transfer resistance. Overall, our strategy realizes scalable sorbent beds with ordered fin-array structures with synergistic enhancement of heat transfer and mass transport for enhancing the water sorption kinetics. We engineered and demonstrated a rapid-cycling SAWH prototype using a commercially available sorbent, i.e., AQSOA Z02. The prototype realizes fast water capture and desorption cycles with high yield water production of 5,826 mLwater kgsorbent–1 day–1.

Experimental Procedures

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Numerical Simulation

A detailed numerical simulation is conducted using COMSOL Multiphysics version 6.0 for adsorption and desorption processes. For the adsorption process, a laminar flow is assigned to simulate the air flow within the millimeter air gaps. The adsorbent coating is modeled as a porous medium. The water vapor diffusion in air and the porous coatings is governed by the convection-diffusion equation, while adsorption of water vapor in the adsorbent crystals is modeled with linear driving force approximation. For the desorption process, the bottom surface is supplied with high-density waste heat. Slightly above the fin tip is a condenser connected with a heat sink. The vapor pressure at the condenser surface is fixed as the saturation pressure to simulate the condensation behavior. More detailed information is available in Note S1, Figures S1 to S4.

Experimental Characterization

Adsorption and desorption characterization results are separately validated with the simulation data using 10 fins coated with zeolite Z02. A fan provides the humid air through the adsorbent bed, and the mass change is monitored during the adsorption process as the water uptake change. After the adsorption, the fins are placed in an enclosed system and heated by cartridge heaters imbedded in the base. The released water vapor is condensed and collected to measure the water desorption, and temperature profiles are recorded at different locations. More detailed information is available in Note S4, Figures S9 to S11.

Data Availability

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All data associated with the study are included in the article and the Supporting Information. Additional information is available from the Lead Contact upon reasonable request.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsenergylett.4c01061.

  • Additional information on adsorbent bed design, simulation, and experimental validation (Figures S1–S11 and Notes S1–S4) (PDF)

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Author Information

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  • Corresponding Authors
    • Xiangyu Li - Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States;  Department of Mechanical Aerospace and Biomedical Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States;  Orcidhttps://orcid.org/0000-0003-0116-7307;  Email: [email protected]
    • Bachir El Fil - Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States;  Email: [email protected]
  • Authors
    • Buxuan Li - Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
    • Gustav Graeber - Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States;  Department of Chemistry, Humboldt-Universität zu Berlin, 12489 Berlin, Germany;  Orcidhttps://orcid.org/0000-0003-0658-6084
    • Adela C. Li - Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
    • Yang Zhong - Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States;  Orcidhttps://orcid.org/0000-0001-6748-903X
    • Mohammed Alshrah - Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
    • Chad T. Wilson - Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
    • Emily Lin - Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
  • Author Contributions

    X.L. and B.E.F. contributed equally to this work. Conceptualization, X.L., B.L., and B.E.F.: Methodology. X.L., B.E.F., and B.L.: Software. X.L., B.L., and G.G.: Investigation. X.L., B.E.F., B.L., G.G., A.C.L., Y.Z., M.A., C.T.W., and E.L.: Writing─original draft. X.L. and B.E.F.: Writing─review and editing. X.L., B.E.F., B.L., G.G., A.L., and Y.Z.: Funding acquisition. X.L. and Y.Z.: Resources. B.E.F.: Supervision. X.L., B.E.

  • Notes
    The authors declare the following competing financial interest(s): B.E.F. and X.L. are the inventors of a provisional patent application based on this work.

Acknowledgments

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We thank our advisor, Dr. Evelyn N. Wang, for her guidance on this work, until the date of her confirmation (Dec. 22, 2022) by the United States Senate to serve as Director of the Advanced Research Projects Agency-Energy (ARPA-E). We also thank Prof. Krista Walton and Dr. Carmen Chen from Georgia Institute of Technology and Prof. Gang Chen, Dr. Arny Leroy, Mr. Cody Jacobucci, Dr. Jiawei Zhou, and Dr. Yaodong Tu from Massachusetts Institute of Technology for valuable discussions. This research was supported by Defense Advanced Research Projects Agency (Award No. HR001120S0014-AWE-PA-035). G.G. acknowledges funding by the Swiss National Science Foundation via a Postdoc Mobility grant (P400P2_194367).

References

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This article references 33 other publications.

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    LaPotin, Alina; Kim, Hyunho; Rao, Sameer R.; Wang, Evelyn N.
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    Atm. H2O harvesting (AWH) is the capture and collection of H2O that is present in the air either as vapor or small H2O droplets. AWH has been recognized as a method for decentralized H2O prodn., esp. in areas where liq. H2O is phys. scarce, or the infrastructure required to bring H2O from other locations is unreliable or infeasible. The main methods of AWH are fog harvesting, dewing, and using sorbent materials to collect vapor from the air. We 1st distinguish between the geog./climatic operating regimes of fog harvesting, dewing, and sorbent-based approaches based on temp. and relative humidity (RH). Because using sorbents has the potential to be more widely applicable to areas which are also facing H2O scarcity, we focus the discussion on this approach. We discuss sorbent materials which have been developed for AWH and the material properties which affect system-level performance. Much of the recent materials development has focused on a single material metric, equil. vapor uptake in (kg of H2O uptake per kg of dry adsorbent), as found from the adsorption isotherm. This equil. property alone, however, is not a good indicator of the actual performance of the AWH system. Understanding material properties which affect heat and mass transport are equally important in the development of materials and components for AWH, because resistances assocd. with heat and mass transport in the bulk material dramatically change the system performance. We focus the discussion on modeling a solar thermal-driven system. Performance of a solar-driven AWH system can be characterized by different metrics, including L of H2O per m2 device per day or L of H2O per kg adsorbent per day. The former metric is esp. important for systems driven by low-grade heat sources because the low power d. of these sources makes this technol. land area intensive. In either case, it is important to include rates in the performance metric to capture the effects of heat and mass transport in the system. We discuss the previously developed modeling framework which can predict the performance of a sorbent material packed into a porous matrix. This model connects mass transport across length scales, considering diffusion both inside a single crystal as well as macroscale geometric parameters, such as the thickness of a composite adsorbent layer. For a simple solar thermal-driven adsorption-based AWH system, we show how this model can be used to optimize the system. Finally, we discuss strategies which have been used to improve heat and mass transport in the design of adsorption systems and the potential for adsorption-based AWH systems for decentralized H2O supplies.
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    A review. Atm. water harvesting (AWH) emerges as a promising means to overcome the water scarcity of arid regions, esp. for inland areas lacking liq. water sources. Beyond conventional system engineering that improves the water yield, novel moisture-harvesting materials provide new aspects to fundamentally promote the AWH technol. benefiting from their high tunability and processability. Innovative material and structural designs enable the moisture harvesters with desirable features, such as high water uptake, facile water collection and long-term recyclability, boosting the rapid development of next-generation AWH. In this Perspective, we first illustrate the sorption mechanism, including absorption and adsorption for moisture-harvesting materials and summarize fundamental requirements, as well as design principles of moisture harvesters. Recent progress on material and structural designs of moisture harvesters for AWH is critically discussed. We conclude with prospective directions for next-generation moisture harvesters to promote AWH from scientific research to practical application.
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    A review. Alternative water resources (seawater, brackish water, atm. water, sewage, etc.) can be converted into clean freshwater via high-efficiency, energy-saving, and cost-effective methods to cope with the global water crisis. Herein, we provide a comprehensive and systematic overview of various solar-powered technologies for alternative water utilization (i.e., "sunlight-energy-water nexus"), including solar-thermal interface desalination (STID), solar-thermal membrane desalination (STMD), solar-driven electrochem. desalination (SED), and solar-thermal atm. water harvesting (ST-AWH). Three strategies have been proposed for improving the evapn. rate of STID systems above the theor. limit and designing all-weather or all-day operating STID systems by analyzing the energy transfer of the evapn. and condensation processes caused by solar-thermal conversion. This also introduces the fundamental principles and current research hotspots of two other solar-driven seawater or brackish water desalination technologies (STMD and SED) in detail. In addn., we also cover ST-AWH and other solar-powered technologies in terms of technol. design, materials evolution, device assembly, etc. Finally, we summarize the content of this comprehensive and discuss the challenges and future outlook of different types of solar-powered alternative water utilization technologies.
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    A review. In the context of global water scarcity, water vapor available in air is a non-negligible supplementary fresh water resource. Current and potential energetically passive procedures for improving atm. water harvesting (AWH) capabilities involve different strategies and dedicated materials, which are reviewed in this paper, from the perspective of morphol. and wettability optimization, substrate cooling, and sorbent assistance. The advantages and limitations of different AWH strategies are resp. discussed, as well as their water harvesting performance. The various applications based on advanced AWH technologies are also demonstrated. A prospective concept of multifunctional water vapor harvesting panel based on promising cooling material, inspired by silicon-based solar energy panels, is finally proposed with a brief outlook of its advantages and challenges.
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    Progress and expectation of atmospheric water harvesting
    Tu, Yaodong; Wang, Ruzhu; Zhang, Yannan; Wang, Jiayun
    Joule (2018), 2 (8), 1452-1475CODEN: JOULBR; ISSN:2542-4351. (Cell Press)
    A review. Even if people live in an arid desert, they know that plenty of water exists in the air they breathe. However, the reality tells us the atm. water cannot help to slake the world's thirst. Thus an important question occurs: what are the fundamental limits of atm. water harvesting that can be achieved in typical arid and semi-arid areas. Here, through a thorough review on the present advances of atm. water-harvesting technologies, we identify the achievements that have been acquired and evaluate the challenges and barriers that retard their applications. Lastly, we clarify our perspectives on how to search for a simple, scalable, yet cost-effective way to produce atm. water for the community and forecast the application of atm. water harvesting in evaporative cooling, such as electronic cooling, power plant cooling, and passive building cooling.
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    Shan, H. All-day Multicyclic Atmospheric Water Harvesting Enabled by Polyelectrolyte Hydrogel with Hybrid Desorption Mode. Adv. Mater. 2023, 35, 2302038,  DOI: 10.1002/adma.202302038
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    23
    All-Day Multicyclic Atmospheric Water Harvesting Enabled by Polyelectrolyte Hydrogel with Hybrid Desorption Mode
    Shan, He; Poredos, Primoz; Ye, Zhanyu; Qu, Hao; Zhang, Yaoxin; Zhou, Mengjuan; Wang, Ruzhu; Tan, Swee Ching
    Advanced Materials (Weinheim, Germany) (2023), 35 (35), 2302038CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Sorption-based atm. water harvesting (AWH) is a promising approach for mitigating worldwide water scarcity. However, reliable water supply driven by sustainable energy regardless of diurnal variation and weather remains a long-standing challenge. To address this issue, a polyelectrolyte hydrogel sorbent with an optimal hybrid-desorption multicyclic-operation strategy is proposed, achieving all-day AWH and a significant increase in daily water prodn. The polyelectrolyte hydrogel possesses a large interior osmotic pressure of 659 atm, which refreshes sorption sites by continuously migrating the sorbed water within its interior, and thus enhancing sorption kinetics. The charged polymeric chains coordinate with hygroscopic salt ions, anchoring the salts and preventing agglomeration and leakage, thereby enhancing cyclic stability. The hybrid desorption mode, which couples solar energy and simulated waste heat, introduces a uniform and adjustable sorbent temp. for achieving all-day ultrafast water release. With rapid sorption-desorption kinetics, an optimization model suggests that eight moisture capture-release cycles are capable of achieving high water yield of 2410 mLwater kgsorbent-1 day-1, up to 3.5 times that of single-cyclic non-hybrid modes. The polyelectrolyte hydrogel sorbent and the coupling with sustainable energy driven desorption mode pave the way for the next-generation AWH systems, significantly bringing freshwater on a multi-kilogram scale closer.
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    Song, Y. High-yield solar-driven atmospheric water harvesting of metal-organic-framework-derived nanoporous carbon with fast-diffusion water channels. Nat. Nanotechnol 2022, 17, 857– 863,  DOI: 10.1038/s41565-022-01135-y
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    High-yield solar-driven atmospheric water harvesting of metal-organic-framework-derived nanoporous carbon with fast-diffusion water channels
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    Nature Nanotechnology (2022), 17 (8), 857-863CODEN: NNAABX; ISSN:1748-3387. (Nature Portfolio)
    Solar-driven, sorption-based atm. water harvesting (AWH) offers a cost-effective soln. to freshwater scarcity in arid areas. Creating AWH devices capable of performing multiple adsorption-desorption cycles per day is crucial for increasing water prodn. rates matching human water requirements. However, achieving rapid-cycling AWH in passive harvesters has been challenging due to sorbents' slow water adsorption-desorption dynamics. Here we report an MOF-derived nanoporous carbon, a sorbent endowed with fast sorption kinetics and excellent photothermal properties, for high-yield AWH. The optimized structure (40% adsorption sites and ∼1.0 nm pore size) has superior sorption kinetics due to the minimized diffusion resistance. Moreover, the carbonaceous sorbent exhibits fast desorption kinetics enabled by efficient solar-thermal heating and high thermal cond. A rapid-cycling water harvester based on nanoporous carbon derived from metal-org. frameworks can produce 0.18 L kgcarbon-1 h-1 of water at 30% relative humidity under one-sun illumination. The proposed design strategy is helpful to develop high-yield, solar-driven AWH for advanced freshwater-generation systems.
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    High-Yield Atmospheric Water Harvesting Device with Integrated Heating/Cooling Enabled by Thermally Tailored Hydrogel Sorbent
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    ACS Energy Letters (2023), 8 (7), 3147-3153CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
    Sorption-based atm. water harvesting (AWH) is regarded as a promising way to produce fresh water in water-stressed areas. However, low water prodn. per unit device mass (WPD) and high energy consumption restrict its applications in portable fresh water replenishment. Here we report a portable high-yield AWH device based on a thermoelec. cell (TEC)-driven integrated heating/cooling thermal design, enabled by a thermally tailored hydrogel sorbent. Heat and cold energies for desorption and condensation are simultaneously generated by the TEC. Graphene oxide-doped sodium alginate hydrogel with high thermal cond. is tailored as the sorbent, which tightly adheres to the TEC's hot region and efficiently takes heat away, for fast desorption as well as temp. control of the TEC. Based on the thermal design of the device and materials, a total WPD of 0.18 L kgdevice-1 h-1 is achieved under 80% RH, almost an order of magnitude higher than that of the traditional design with the same energy input.
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    Improving atmospheric water production yield: Enabling multiple water harvesting cycles with nano sorbent
    Li, Renyuan; Shi, Yusuf; Wu, Mengchun; Hong, Seunghyun; Wang, Peng
    Nano Energy (2020), 67 (), 104255CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)
    Clean water shortage has long been a challenge in remote and landlocked communities esp. for the impoverished. Atm. water is now considered as an unconventional but accessible fresh water source and sorption-based atm. water generator (AWG) has been successfully demonstrated a reliable way of harvesting atm. water. The water vapor sorbents with high water uptake capacity and esp. fast vapor sorption/desorption kinetics have become the bottleneck to a desirable clean water productivity in AWG. In this work, we developed a new nano vapor sorbent composed of a nano carbon hollow capsule with LiCl inside the void core. The sorbent can capture water vapor from ambient air as much as 100% of its own wt. under RH 60% within 3 h and quickly release the sorbed water within just half hour under 1 kW/m2 sunlight irradn. A batch-mode AWG device was able to conduct 3 sorption/desorption cycles within 10 h during one day test in the outdoor condition and produced 1.6 kgwater/kgsorbent. A prototype of continuous AWG device was designed, fabricated, and successfully demonstrated, hinting a possible way of large-scale deployment of AWG for practical purposes.
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    Zhou, X.; Lu, H.; Zhao, F.; Yu, G. Atmospheric Water Harvesting: A Review of Material and Structural Designs. ACS Mater. Lett. 2020, 2, 671– 684,  DOI: 10.1021/acsmaterialslett.0c00130
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    Atmospheric Water Harvesting: A Review of Material and Structural Designs
    Zhou, Xingyi; Lu, Hengyi; Zhao, Fei; Yu, Guihua
    ACS Materials Letters (2020), 2 (7), 671-684CODEN: AMLCEF; ISSN:2639-4979. (American Chemical Society)
    A review. Atm. water harvesting (AWH) emerges as a promising means to overcome the water scarcity of arid regions, esp. for inland areas lacking liq. water sources. Beyond conventional system engineering that improves the water yield, novel moisture-harvesting materials provide new aspects to fundamentally promote the AWH technol. benefiting from their high tunability and processability. Innovative material and structural designs enable the moisture harvesters with desirable features, such as high water uptake, facile water collection and long-term recyclability, boosting the rapid development of next-generation AWH. In this Perspective, we first illustrate the sorption mechanism, including absorption and adsorption for moisture-harvesting materials and summarize fundamental requirements, as well as design principles of moisture harvesters. Recent progress on material and structural designs of moisture harvesters for AWH is critically discussed. We conclude with prospective directions for next-generation moisture harvesters to promote AWH from scientific research to practical application.
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    LaPotin, A.; Kim, H.; Rao, S. R.; Wang, E. N. Adsorption-Based Atmospheric Water Harvesting: Impact of Material and Component Properties on System-Level Performance. Acc. Chem. Res. 2019, 52, 1588– 1597,  DOI: 10.1021/acs.accounts.9b00062
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    Adsorption-Based Atmospheric Water Harvesting: Impact of Material and Component Properties on System-Level Performance
    LaPotin, Alina; Kim, Hyunho; Rao, Sameer R.; Wang, Evelyn N.
    Accounts of Chemical Research (2019), 52 (6), 1588-1597CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    Atm. H2O harvesting (AWH) is the capture and collection of H2O that is present in the air either as vapor or small H2O droplets. AWH has been recognized as a method for decentralized H2O prodn., esp. in areas where liq. H2O is phys. scarce, or the infrastructure required to bring H2O from other locations is unreliable or infeasible. The main methods of AWH are fog harvesting, dewing, and using sorbent materials to collect vapor from the air. We 1st distinguish between the geog./climatic operating regimes of fog harvesting, dewing, and sorbent-based approaches based on temp. and relative humidity (RH). Because using sorbents has the potential to be more widely applicable to areas which are also facing H2O scarcity, we focus the discussion on this approach. We discuss sorbent materials which have been developed for AWH and the material properties which affect system-level performance. Much of the recent materials development has focused on a single material metric, equil. vapor uptake in (kg of H2O uptake per kg of dry adsorbent), as found from the adsorption isotherm. This equil. property alone, however, is not a good indicator of the actual performance of the AWH system. Understanding material properties which affect heat and mass transport are equally important in the development of materials and components for AWH, because resistances assocd. with heat and mass transport in the bulk material dramatically change the system performance. We focus the discussion on modeling a solar thermal-driven system. Performance of a solar-driven AWH system can be characterized by different metrics, including L of H2O per m2 device per day or L of H2O per kg adsorbent per day. The former metric is esp. important for systems driven by low-grade heat sources because the low power d. of these sources makes this technol. land area intensive. In either case, it is important to include rates in the performance metric to capture the effects of heat and mass transport in the system. We discuss the previously developed modeling framework which can predict the performance of a sorbent material packed into a porous matrix. This model connects mass transport across length scales, considering diffusion both inside a single crystal as well as macroscale geometric parameters, such as the thickness of a composite adsorbent layer. For a simple solar thermal-driven adsorption-based AWH system, we show how this model can be used to optimize the system. Finally, we discuss strategies which have been used to improve heat and mass transport in the design of adsorption systems and the potential for adsorption-based AWH systems for decentralized H2O supplies.
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    El Fil, B.; Li, X.; Díaz-Marín, C. D.; Zhang, L.; Jacobucci, C. L. Significant enhancement of sorption kinetics via boiling-assisted channel templating. Cell Rep. Phys. Sci. 2023, 4, 101549,  DOI: 10.1016/j.xcrp.2023.101549
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  • Abstract

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    Figure 1

    Figure 1. Comparison between solar-driven (passive) and high-energy-driven SAWH devices. (A) SAWH designs driven by solar energy. Limited by solar energy density, the adsorption/desorption cycle often synchronizes with the day–night cycle, resulting in a small amount of daily water production. (B) High-density energy sources to drive SAWH include electricity, biomass combustion, or various sources of waste heat. With high-density energy to drive desorption, multicyclic operation with thinner coatings achieves faster kinetics and higher daily water production.

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    Figure 2

    Figure 2. Adsorbent bed design considerations. (A) Optimization of kinetics and compactness for atmospheric water harvesting with single-layer coatings. Humid air flows above the coating surface. Thin coatings enable fast kinetics and multicyclic operation but sacrifice the compactness. (B) Compact adsorbent bed design with an array of adsorbent fins (arranged in the x-axis), consisting of metal sheets and adsorbent coatings. Humid air flows through the air gaps (along the y-axis) between the adsorbent fins. (C) Front view during the adsorption and desorption processes. During adsorption, humid air enters the air channels and water vapor is adsorbed into the coating, illustrated by blue arrows. During desorption, the sorbent coating is heated by thermal energy input from the base along the z-axis. Desorbed water vapor is represented by dashed blue arrows.

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    Figure 3

    Figure 3. Adsorption simulation results. (A) Water vapor transport path and associated mass transport resistance. (B) Transient water uptake of adsorbent with different air flow velocities. (C) Outlet air flow humidity with different air gap thicknesses and air velocities. (D) Water uptake as a function of different air velocities and air gap thicknesses. Optimized air gaps are identified, as a trade-off between vapor supply and diffusion resistance in the air channels.

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    Figure 4

    Figure 4. Desorption simulation results. (A) Temperature profile and (B) adsorbent water uptake profile at 300 s after the start of desorption. (C) Temperature and water uptake response during the desorption operation. Red and green curves represent the average temperatures of adsorbent and condenser, and the blue dashed curve represents water uptake in the adsorbent. In the first 50 s, thermal energy diffuses through the fins, before the adsorbent reaches its desorption temperature. As the temperature increases, water vapor is desorbed, increasing the condenser temperature and reducing the water uptake. Due to the constant heat flux, the desorption rate is mostly linear, until the adsorbent is further heated at the end of desorption.

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    Figure 5

    Figure 5. Experimental validation of adsorption and desorption for AQSOA Z02 adsorption bed. (A) Experimental validation setup of adsorption process, where water adsorption is monitored with weight. (B) Experimental validation setup of the desorption process in an enclosed system, where heat is provided with cartridge heaters. Experimental results are compared with numerical models for (C) adsorption and (D) desorption processes. Experimental and modeling adsorption data are represented by blue solid line and black dashed line, respectively.

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    Figure 6

    Figure 6. Water sorption and kinetics in the fin-structured adsorbent bed. (A) Schematic showing humid air flowing through the air gap between adsorbent coatings. (B) Design map showing the water uptake as a function of the product of equilibrium water uptake of the adsorbent and its kinetics, weqDμ/R2, and the time scale of mass transfer in the sorbent coating (δads2ε3/2Dv). (C) Water uptake as a function of time as a function of equilibrium uptake, intracrystalline diffusivity, and coating thickness. (D) Cumulative amount of daily water collection for different sorbent characteristics and thicknesses.

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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXjvVGhtLw%253D&md5=48712a73f36b3ad3e35b87bd03fd4f04
    4. 4
      Wahlgren, R. V. Atmospheric water vapour processor designs for potable water production: a review. Water Res. 2001, 35, 1– 22,  DOI: 10.1016/S0043-1354(00)00247-5
      4
      Atmospheric water vapour processor designs for potable water production: a review
      Wahlgren R V
      Water research (2001), 35 (1), 1-22 ISSN:0043-1354.
      Atmospheric water vapour processing (AWVP) technology is reviewed. These processors are machines which extract water molecules from the atmosphere, ultimately causing a phase change from vapour to liquid. Three classes of machines have been proposed. The machines either cool a surface below the dewpoint of the ambient air, concentrate water vapour through use of solid or liquid desiccants, or induce and control convection in a tower structure. Patented devices vary in scale and potable water output from small units suitable for one person's daily needs to structures as large as multi-story office buildings capable of supplying drinking water to an urban neighbourhood. Energy and mass cascades (flowcharts) are presented for the three types of water vapour processors. The flowcharts assist in classifying designs and discussing their strengths and limitations. Practicality and appropriateness of the various designs for contributing to water supplies are considered along with water cost estimates. Prototypes that have been tested successfully are highlighted. Absolute humidity (meteorological normals) ranges from 4.0 g of water vapour per cubic metre of surface air in the atmosphere (Las Vegas, Nevada, USA) to 21.2 g m-3 (Djibouti, Republic of Djibouti). Antofagasta, Chile has a normal absolute humidity of 10.9 g m-3. A 40% efficient machine in the vicinity of Antofagasta requires an airflow of 10 m3 s-1 to produce 3767 l of water per day. At a consumption of 50 l per person per day, 75 people could have basic water requirements for drinking, sanitation, bathing, and cooking met by a decentralized and simplified water supply infrastructure with attendant economic and societal benefits.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD3M3gslCjuw%253D%253D&md5=249596dbf9c5ed3ad367cb7990042ea7
    5. 5
      Kim, H. Water harvesting from air with metal-organic frameworks powered by natural sunlight. Science (1979) 2017, 356, 430– 434,  DOI: 10.1126/science.aam8743
      5
      Water harvesting from air with metal-organic frameworks powered by natural sunlight
      Kim, Hyunho; Yang, Sungwoo; Rao, Sameer R.; Narayanan, Shankar; Kapustin, Eugene A.; Furukawa, Hiroyasu; Umans, Ari S.; Yaghi, Omar M.; Wang, Evelyn N.
      Science (Washington, DC, United States) (2017), 356 (6336), 430-434CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      Atm. water is a resource equiv. to -10% of all fresh water in lakes on Earth. However, an efficient process for capturing and delivering water from air, esp. at low humidity levels (down to 20%), has not been developed. We report the design and demonstration of a device based on a porous metal-org. framework {M0F-801, [Zr604(0H)4(fumarate)6]} that captures water from the atm. at ambient conditions by using low-grade heat from natural sunlight at a flux of less than 1 sun (1 kW per square meter). This device is capable of harvesting 2.8 L of water per kg of MOF daily at relative humidity levels as low as 20% and requires no addnl. input of energy.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmvFejtLo%253D&md5=14666dd987441772addcc6bf9c70b02a
    6. 6
      Kim, H. Adsorption-based atmospheric water harvesting device for arid climates. Nat. Commun. 2018, 9, 1191,  DOI: 10.1038/s41467-018-03162-7
      6
      Adsorption-based atmospheric water harvesting device for arid climates
      Kim Hyunho; Rao Sameer R; Zhao Lin; Yang Sungwoo; Wang Evelyn N; Kapustin Eugene A; Yaghi Omar M; Kapustin Eugene A; Yaghi Omar M; Yaghi Omar M
      Nature communications (2018), 9 (1), 1191 ISSN:.
      Water scarcity is a particularly severe challenge in arid and desert climates. While a substantial amount of water is present in the form of vapour in the atmosphere, harvesting this water by state-of-the-art dewing technology can be extremely energy intensive and impractical, particularly when the relative humidity (RH) is low (i.e., below ~40% RH). In contrast, atmospheric water generators that utilise sorbents enable capture of vapour at low RH conditions and can be driven by the abundant source of solar-thermal energy with higher efficiency. Here, we demonstrate an air-cooled sorbent-based atmospheric water harvesting device using the metal-organic framework (MOF)-801 [Zr6O4(OH)4(fumarate)6] operating in an exceptionally arid climate (10-40% RH) and sub-zero dew points (Tempe, Arizona, USA) with a thermal efficiency (solar input to water conversion) of ~14%. We predict that this device delivered over 0.25 L of water per kg of MOF for a single daily cycle.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1MnjvF2ntQ%253D%253D&md5=fb48621865bb8a88140d8d6f5cbc3b31
    7. 7
      Hanikel, N. Rapid Cycling and Exceptional Yield in a Metal-Organic Framework Water Harvester. ACS Cent Sci. 2019, 5, 1699– 1706,  DOI: 10.1021/acscentsci.9b00745
      7
      Rapid Cycling and Exceptional Yield in a Metal-Organic Framework Water Harvester
      Hanikel, Nikita; Prevot, Mathieu S.; Fathieh, Farhad; Kapustin, Eugene A.; Lyu, Hao; Wang, Haoze; Diercks, Nicolas J.; Glover, T. Grant; Yaghi, Omar M.
      ACS Central Science (2019), 5 (10), 1699-1706CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
      Sorbent-assisted water harvesting from air represents an attractive way to address water scarcity in arid climates. Hitherto, sorbents developed for this technol. have exclusively been designed to perform one water harvesting cycle (WHC) per day, but the productivities attained with this approach cannot reasonably meet the rising demand for drinking water. This work shows that a microporous aluminum-based metal-org. framework, MOF-303, can perform an adsorption-desorption cycle within minutes under a mild temp. swing, which opens the way for high-productivity water harvesting through rapid, continuous WHCs. Addnl., the favorable dynamic water sorption properties of MOF-303 allow it to outperform other com. sorbents displaying excellent steady-state characteristics under similar exptl. conditions. Finally, these findings are implemented in a new water harvester capable of generating 1.3 L kgMOF-1 day-1 in an indoor arid environment (32% relative humidity, 27°C) and 0.7 L kgMOF-1 day-1 in the Mojave Desert (in conditions as extreme as 10% RH, 27°C), representing an improvement by 1 order of magnitude over previously reported devices. This study demonstrates that creating sorbents capable of rapid water sorption dynamics, rather than merely focusing on high water capacities, is crucial to reach water prodn. on a scale matching human consumption.
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    8. 8
      LaPotin, A. Dual-Stage Atmospheric Water Harvesting Device for Scalable Solar-Driven Water Production. Joule 2021, 5, 166,  DOI: 10.1016/j.joule.2020.09.008
      8
      Dual-Stage Atmospheric Water Harvesting Device for Scalable Solar-Driven Water Production
      LaPotin, Alina; Zhong, Yang; Zhang, Lenan; Zhao, Lin; Leroy, Arny; Kim, Hyunho; Rao, Sameer R.; Wang, Evelyn N.
      Joule (2021), 5 (1), 166-182CODEN: JOULBR; ISSN:2542-4351. (Cell Press)
      Recent work has demonstrated adsorption-based solar-thermal-driven atm. water harvesting (AWH) in arid regions, but the daily water productivity (L/m2/day) of devices remains low. We developed and tested a dual-stage AWH device with optimized transport. By recovering the latent heat of condensation of the top stage and maintaining the required temp. difference between stages, the design enables higher daily water productivity than a single-stage device without auxiliary units for heating or vapor transport. In outdoor expts., we demonstrated a dual-stage water harvesting device using com. zeolite (AQSOA Z01) and regeneration under natural, unconcd. sunlight where ∼0.77 L/m2/day of water was harvested. Our modeling showed that by further increasing top-stage temps. via design modifications, approx. twice the daily productivity of the single-stage configuration can be achieved. This dual-stage device configuration is a promising design approach to achieve high performance, scalable, and low-cost solar-thermal AWH.
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    9. 9
      Shan, H. Exceptional water production yield enabled by batch-processed portable water harvester in semi-arid climate. Nat. Commun. 2022, 13, 5406,  DOI: 10.1038/s41467-022-33062-w
      9
      Exceptional water production yield enabled by batch-processed portable water harvester in semi-arid climate
      Shan, He; Li, Chunfeng; Chen, Zhihui; Ying, Wenjun; Poredos, Primoz; Ye, Zhanyu; Pan, Quanwen; Wang, Jiayun; Wang, Ruzhu
      Nature Communications (2022), 13 (1), 5406CODEN: NCAOBW; ISSN:2041-1723. (Nature Portfolio)
      Sorption-based atm. water harvesting has the potential to realize water prodn. anytime, anywhere, but reaching a hundred-gram high water yield in semi-arid climates is still challenging, although state-of-the-art sorbents have been used. Here, we report a portable and modularized water harvester with scalable, low-cost, and lightwt. LiCl-based hygroscopic composite (Li-SHC) sorbents. Li-SHC achieves water uptake capacity of 1.18, 1.79, and 2.93 g g-1 at 15%, 30%, and 60% RH, resp. Importantly, considering the large mismatch between water capture and release rates, a rationally designed batch processing mode is proposed to pursue max. water yield in a single diurnal cycle. Together with the advanced thermal design, the water harvester shows an exceptional water yield of 311.69 g day-1 and 1.09 g gsorbent-1 day-1 in the semi-arid climate with the extremely low RH of ∼15%, demonstrating the adaptability and possibility of achieving large-scale and reliable water prodn. in real scenarios.
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    10. 10
      Xu, J. Efficient Solar-Driven Water Harvesting from Arid Air with Metal-Organic Frameworks Modified by Hygroscopic Salt. Angewandte Chemie - International Edition 2020, 59, 5202– 5210,  DOI: 10.1002/anie.201915170
      There is no corresponding record for this reference.
    11. 11
      LaPotin, A.; Kim, H.; Rao, S. R.; Wang, E. N. Adsorption-Based Atmospheric Water Harvesting: Impact of Material and Component Properties on System-Level Performance. Acc. Chem. Res. 2019, 52, 1588– 1597,  DOI: 10.1021/acs.accounts.9b00062
      11
      Adsorption-Based Atmospheric Water Harvesting: Impact of Material and Component Properties on System-Level Performance
      LaPotin, Alina; Kim, Hyunho; Rao, Sameer R.; Wang, Evelyn N.
      Accounts of Chemical Research (2019), 52 (6), 1588-1597CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      Atm. H2O harvesting (AWH) is the capture and collection of H2O that is present in the air either as vapor or small H2O droplets. AWH has been recognized as a method for decentralized H2O prodn., esp. in areas where liq. H2O is phys. scarce, or the infrastructure required to bring H2O from other locations is unreliable or infeasible. The main methods of AWH are fog harvesting, dewing, and using sorbent materials to collect vapor from the air. We 1st distinguish between the geog./climatic operating regimes of fog harvesting, dewing, and sorbent-based approaches based on temp. and relative humidity (RH). Because using sorbents has the potential to be more widely applicable to areas which are also facing H2O scarcity, we focus the discussion on this approach. We discuss sorbent materials which have been developed for AWH and the material properties which affect system-level performance. Much of the recent materials development has focused on a single material metric, equil. vapor uptake in (kg of H2O uptake per kg of dry adsorbent), as found from the adsorption isotherm. This equil. property alone, however, is not a good indicator of the actual performance of the AWH system. Understanding material properties which affect heat and mass transport are equally important in the development of materials and components for AWH, because resistances assocd. with heat and mass transport in the bulk material dramatically change the system performance. We focus the discussion on modeling a solar thermal-driven system. Performance of a solar-driven AWH system can be characterized by different metrics, including L of H2O per m2 device per day or L of H2O per kg adsorbent per day. The former metric is esp. important for systems driven by low-grade heat sources because the low power d. of these sources makes this technol. land area intensive. In either case, it is important to include rates in the performance metric to capture the effects of heat and mass transport in the system. We discuss the previously developed modeling framework which can predict the performance of a sorbent material packed into a porous matrix. This model connects mass transport across length scales, considering diffusion both inside a single crystal as well as macroscale geometric parameters, such as the thickness of a composite adsorbent layer. For a simple solar thermal-driven adsorption-based AWH system, we show how this model can be used to optimize the system. Finally, we discuss strategies which have been used to improve heat and mass transport in the design of adsorption systems and the potential for adsorption-based AWH systems for decentralized H2O supplies.
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    12. 12
      Furukawa, H. Water adsorption in porous metal-organic frameworks and related materials. J. Am. Chem. Soc. 2014, 136, 4369– 4381,  DOI: 10.1021/ja500330a
      12
      Water Adsorption in Porous Metal-Organic Frameworks and Related Materials
      Furukawa, Hiroyasu; Gandara, Felipe; Zhang, Yue-Biao; Jiang, Juncong; Queen, Wendy L.; Hudson, Matthew R.; Yaghi, Omar M.
      Journal of the American Chemical Society (2014), 136 (11), 4369-4381CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Three criteria for achieving high performing porous materials for water adsorption have been identified. These criteria deal with condensation pressure of water in the pores, uptake capacity, and recyclability and water stability of the material. Water adsorption properties of 23 materials were investigated, 20 of which being metal-org. frameworks (MOFs). Among the MOFs were 10 zirconium(IV) MOFs with a subset of these, MOF-801-SC (single crystal form), -802, -805, -806, -808, -812, and -841 reported for the first time. MOF-801-P (microcryst. powder form) was reported earlier and studied here for its water adsorption properties. MOF-812 was only made and structurally characterized but not examd. for water adsorption because it is a byproduct of MOF-841 synthesis. All the new zirconium MOFs are made from the Zr6O4(OH)4(-CO2) secondary building units (n = 6, 8, 10, or 12) and variously shaped carboxyl org. linkers to make extended porous frameworks. The permanent porosity of all 23 materials was confirmed and their water adsorption measured to reveal that MOF-801-P and MOF-841 are the highest performers based on the three criteria stated above; they are water stable, do not lose capacity after five adsorption/desorption cycles, and are easily regenerated at room temp. An X-ray single-crystal study and a powder neutron diffraction study reveal the position of the water adsorption sites in MOF-801 and highlight the importance of the intermol. interaction between adsorbed water mols. within the pores.
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    13. 13
      Poredoš, P.; Wang, R. Sustainable cooling with water generation. Science (1979) 2023, 380, 458– 459,  DOI: 10.1126/science.add1795
      There is no corresponding record for this reference.
    14. 14
      Zhou, X.; Lu, H.; Zhao, F.; Yu, G. Atmospheric Water Harvesting: A Review of Material and Structural Designs. ACS Mater. Lett. 2020, 2, 671– 684,  DOI: 10.1021/acsmaterialslett.0c00130
      14
      Atmospheric Water Harvesting: A Review of Material and Structural Designs
      Zhou, Xingyi; Lu, Hengyi; Zhao, Fei; Yu, Guihua
      ACS Materials Letters (2020), 2 (7), 671-684CODEN: AMLCEF; ISSN:2639-4979. (American Chemical Society)
      A review. Atm. water harvesting (AWH) emerges as a promising means to overcome the water scarcity of arid regions, esp. for inland areas lacking liq. water sources. Beyond conventional system engineering that improves the water yield, novel moisture-harvesting materials provide new aspects to fundamentally promote the AWH technol. benefiting from their high tunability and processability. Innovative material and structural designs enable the moisture harvesters with desirable features, such as high water uptake, facile water collection and long-term recyclability, boosting the rapid development of next-generation AWH. In this Perspective, we first illustrate the sorption mechanism, including absorption and adsorption for moisture-harvesting materials and summarize fundamental requirements, as well as design principles of moisture harvesters. Recent progress on material and structural designs of moisture harvesters for AWH is critically discussed. We conclude with prospective directions for next-generation moisture harvesters to promote AWH from scientific research to practical application.
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    15. 15
      Lu, H. Materials Engineering for Atmospheric Water Harvesting: Progress and Perspectives. Adv. Mater. 2022, 34, 2110079,  DOI: 10.1002/adma.202110079
      15
      Materials Engineering for Atmospheric Water Harvesting: Progress and Perspectives
      Lu, Hengyi; Shi, Wen; Guo, Youhong; Guan, Weixin; Lei, Chuxin; Yu, Guihua
      Advanced Materials (Weinheim, Germany) (2022), 34 (12), 2110079CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Atm. water harvesting (AWH) is emerging as a promising strategy to produce fresh water from abundant airborne moisture to overcome the global clean water shortage. The ubiquitous moisture resources allow AWH to be free from geog. restrictions and potentially realize decentralized applications, making it a vital parallel or supplementary freshwater prodn. approach to liq. water resource-based technologies. Recent advances in regulating chem. properties and micro/nanostructures of moisture-harvesting materials have demonstrated new possibilities to promote enhanced device performance and new understandings. This perspective aims to provide a timely overview on the state-of-the-art materials design and how they serve as the active components in AWH. First, the key processes of AWH, including vapor condensation, droplet nucleation, growth, and departure are outlined, and the desired material properties based on the fundamental mechanisms are discussed. Then, how tailoring materials-water interactions at the mol. level play a vital role in realizing high water uptake and low energy consumption is shown. Last, the challenges and outlook on further improving AWH from material designs and system engineering aspects are highlighted.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XivV2hs74%253D&md5=8f21b8568405261a6570bfcf512b3b92
    16. 16
      Logan, M. W.; Langevin, S.; Xia, Z. Reversible Atmospheric Water Harvesting Using Metal-Organic Frameworks. Sci. Rep 2020, 10, 1492,  DOI: 10.1038/s41598-020-58405-9
      16
      Reversible Atmospheric Water Harvesting Using Metal-Organic Frameworks
      Logan, Matthew W.; Langevin, Spencer; Xia, Zhiyong
      Scientific Reports (2020), 10 (1), 1492CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)
      The passive capture of clean water from humid air without reliance on bulky equipment and high energy has been a substantial challenge and has attracted significant interest as a potential environmentally friendly alternative to traditional water harvesting methods. Metal-org. frameworks (MOFs) offer a high potential for this application due to their structural versatility which permits scalable, facile modulations of structural and functional elements. Although MOFs are promising materials for water harvesting, little research has been done to address the microstructure-adsorbing characteristics relationship with respect to the dynamic adsorption-desorption process. In this article, we present a parametric study of nine hydrolytically stable MOFs with diverse structures for unraveling fundamental material properties that govern the kinetics of water sequestration in this class of materials as well as investigating overall uptake capacity gravimetrically. The effects of temp., relative humidity, and powder bed thickness on the adsorption-desorption process are explored for achieving optimal operational parameters. We found that Zr-MOF-808 can produce up to 8.66 LH2O kg-1MOF day-1, an extraordinary finding that outperforms any previously reported values for MOF-based systems. The presented findings help to deepen our understanding and guide the discovery of next-generation water harvesting materials.
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    17. 17
      Rieth, A. J.; Yang, S.; Wang, E. N.; Dincǎ, M. Record Atmospheric Fresh Water Capture and Heat Transfer with a Material Operating at the Water Uptake Reversibility Limit. ACS Cent Sci. 2017, 3, 668– 672,  DOI: 10.1021/acscentsci.7b00186
      17
      Record Atmospheric Fresh Water Capture and Heat Transfer with a Material Operating at the Water Uptake Reversibility Limit
      Rieth, Adam J.; Yang, Sungwoo; Wang, Evelyn N.; Dinca, Mircea
      ACS Central Science (2017), 3 (6), 668-672CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)
      The capture of water vapor at low relative humidity is desirable for producing potable water in desert regions and for heat transfer and storage. Here, we report a mesoporous metal-org. framework that captures 82% water by wt. below 30% relative humidity. Under simulated desert conditions, the sorbent would deliver 0.82 gH2O gMOF-1, nearly double the quantity of fresh water compared to the previous best material. The material further demonstrates a cooling capacity of 400 kWh m-3 per cycle, also a record value for a sorbent capable of creating a 20 °C difference between ambient and output temp. The water uptake in this sorbent is optimized: the pore diam. of our material is above the crit. diam. for water capillary action, enabling water uptake at the limit of reversibility.
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    18. 18
      Li, Z. Solar-Powered Sustainable Water Production: State-of-the-Art Technologies for Sunlight-Energy-Water Nexus. ACS Nano 2021, 15, 12535– 12566,  DOI: 10.1021/acsnano.1c01590
      18
      Solar-Powered Sustainable Water Production: State-of-the-Art Technologies for Sunlight-Energy-Water Nexus
      Li, Zhengtong; Xu, Xingtao; Sheng, Xinran; Lin, Peng; Tang, Jing; Pan, Likun; Kaneti, Yusuf Valentino; Yang, Tao; Yamauchi, Yusuke
      ACS Nano (2021), 15 (8), 12535-12566CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      A review. Alternative water resources (seawater, brackish water, atm. water, sewage, etc.) can be converted into clean freshwater via high-efficiency, energy-saving, and cost-effective methods to cope with the global water crisis. Herein, we provide a comprehensive and systematic overview of various solar-powered technologies for alternative water utilization (i.e., "sunlight-energy-water nexus"), including solar-thermal interface desalination (STID), solar-thermal membrane desalination (STMD), solar-driven electrochem. desalination (SED), and solar-thermal atm. water harvesting (ST-AWH). Three strategies have been proposed for improving the evapn. rate of STID systems above the theor. limit and designing all-weather or all-day operating STID systems by analyzing the energy transfer of the evapn. and condensation processes caused by solar-thermal conversion. This also introduces the fundamental principles and current research hotspots of two other solar-driven seawater or brackish water desalination technologies (STMD and SED) in detail. In addn., we also cover ST-AWH and other solar-powered technologies in terms of technol. design, materials evolution, device assembly, etc. Finally, we summarize the content of this comprehensive and discuss the challenges and future outlook of different types of solar-powered alternative water utilization technologies.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsFKhsL3K&md5=100ad5db1056569518917de73c239b43
    19. 19
      Humphrey, J. H. The potential for atmospheric water harvesting to accelerate household access to safe water. Lancet Planet. Health 2020, 4, e91– e92,  DOI: 10.1016/S2542-5196(20)30034-6
      There is no corresponding record for this reference.
    20. 20
      Liu, X.; Beysens, D.; Bourouina, T. Water Harvesting from Air: Current Passive Approaches and Outlook. ACS Mater. Lett. 2022, 4, 1003– 1024,  DOI: 10.1021/acsmaterialslett.1c00850
      20
      Water Harvesting from Air: Current Passive Approaches and Outlook
      Liu, Xiaoyi; Beysens, Daniel; Bourouina, Tarik
      ACS Materials Letters (2022), 4 (5), 1003-1024CODEN: AMLCEF; ISSN:2639-4979. (American Chemical Society)
      A review. In the context of global water scarcity, water vapor available in air is a non-negligible supplementary fresh water resource. Current and potential energetically passive procedures for improving atm. water harvesting (AWH) capabilities involve different strategies and dedicated materials, which are reviewed in this paper, from the perspective of morphol. and wettability optimization, substrate cooling, and sorbent assistance. The advantages and limitations of different AWH strategies are resp. discussed, as well as their water harvesting performance. The various applications based on advanced AWH technologies are also demonstrated. A prospective concept of multifunctional water vapor harvesting panel based on promising cooling material, inspired by silicon-based solar energy panels, is finally proposed with a brief outlook of its advantages and challenges.
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    21. 21
      Ejeian, M.; Wang, R. Z. Adsorption-based atmospheric water harvesting. Joule 2021, 5, 1678– 1703,  DOI: 10.1016/j.joule.2021.04.005
      There is no corresponding record for this reference.
    22. 22
      Tu, Y.; Wang, R.; Zhang, Y.; Wang, J. Progress and Expectation of Atmospheric Water Harvesting. Joule 2018, 2, 1452– 1475,  DOI: 10.1016/j.joule.2018.07.015
      22
      Progress and expectation of atmospheric water harvesting
      Tu, Yaodong; Wang, Ruzhu; Zhang, Yannan; Wang, Jiayun
      Joule (2018), 2 (8), 1452-1475CODEN: JOULBR; ISSN:2542-4351. (Cell Press)
      A review. Even if people live in an arid desert, they know that plenty of water exists in the air they breathe. However, the reality tells us the atm. water cannot help to slake the world's thirst. Thus an important question occurs: what are the fundamental limits of atm. water harvesting that can be achieved in typical arid and semi-arid areas. Here, through a thorough review on the present advances of atm. water-harvesting technologies, we identify the achievements that have been acquired and evaluate the challenges and barriers that retard their applications. Lastly, we clarify our perspectives on how to search for a simple, scalable, yet cost-effective way to produce atm. water for the community and forecast the application of atm. water harvesting in evaporative cooling, such as electronic cooling, power plant cooling, and passive building cooling.
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    23. 23
      Shan, H. All-day Multicyclic Atmospheric Water Harvesting Enabled by Polyelectrolyte Hydrogel with Hybrid Desorption Mode. Adv. Mater. 2023, 35, 2302038,  DOI: 10.1002/adma.202302038
      23
      All-Day Multicyclic Atmospheric Water Harvesting Enabled by Polyelectrolyte Hydrogel with Hybrid Desorption Mode
      Shan, He; Poredos, Primoz; Ye, Zhanyu; Qu, Hao; Zhang, Yaoxin; Zhou, Mengjuan; Wang, Ruzhu; Tan, Swee Ching
      Advanced Materials (Weinheim, Germany) (2023), 35 (35), 2302038CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Sorption-based atm. water harvesting (AWH) is a promising approach for mitigating worldwide water scarcity. However, reliable water supply driven by sustainable energy regardless of diurnal variation and weather remains a long-standing challenge. To address this issue, a polyelectrolyte hydrogel sorbent with an optimal hybrid-desorption multicyclic-operation strategy is proposed, achieving all-day AWH and a significant increase in daily water prodn. The polyelectrolyte hydrogel possesses a large interior osmotic pressure of 659 atm, which refreshes sorption sites by continuously migrating the sorbed water within its interior, and thus enhancing sorption kinetics. The charged polymeric chains coordinate with hygroscopic salt ions, anchoring the salts and preventing agglomeration and leakage, thereby enhancing cyclic stability. The hybrid desorption mode, which couples solar energy and simulated waste heat, introduces a uniform and adjustable sorbent temp. for achieving all-day ultrafast water release. With rapid sorption-desorption kinetics, an optimization model suggests that eight moisture capture-release cycles are capable of achieving high water yield of 2410 mLwater kgsorbent-1 day-1, up to 3.5 times that of single-cyclic non-hybrid modes. The polyelectrolyte hydrogel sorbent and the coupling with sustainable energy driven desorption mode pave the way for the next-generation AWH systems, significantly bringing freshwater on a multi-kilogram scale closer.
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    24. 24
      Song, Y. High-yield solar-driven atmospheric water harvesting of metal-organic-framework-derived nanoporous carbon with fast-diffusion water channels. Nat. Nanotechnol 2022, 17, 857– 863,  DOI: 10.1038/s41565-022-01135-y
      24
      High-yield solar-driven atmospheric water harvesting of metal-organic-framework-derived nanoporous carbon with fast-diffusion water channels
      Song, Yan; Xu, Ning; Liu, Guoliang; Qi, Heshan; Zhao, Wei; Zhu, Bin; Zhou, Lin; Zhu, Jia
      Nature Nanotechnology (2022), 17 (8), 857-863CODEN: NNAABX; ISSN:1748-3387. (Nature Portfolio)
      Solar-driven, sorption-based atm. water harvesting (AWH) offers a cost-effective soln. to freshwater scarcity in arid areas. Creating AWH devices capable of performing multiple adsorption-desorption cycles per day is crucial for increasing water prodn. rates matching human water requirements. However, achieving rapid-cycling AWH in passive harvesters has been challenging due to sorbents' slow water adsorption-desorption dynamics. Here we report an MOF-derived nanoporous carbon, a sorbent endowed with fast sorption kinetics and excellent photothermal properties, for high-yield AWH. The optimized structure (40% adsorption sites and ∼1.0 nm pore size) has superior sorption kinetics due to the minimized diffusion resistance. Moreover, the carbonaceous sorbent exhibits fast desorption kinetics enabled by efficient solar-thermal heating and high thermal cond. A rapid-cycling water harvester based on nanoporous carbon derived from metal-org. frameworks can produce 0.18 L kgcarbon-1 h-1 of water at 30% relative humidity under one-sun illumination. The proposed design strategy is helpful to develop high-yield, solar-driven AWH for advanced freshwater-generation systems.
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    25. 25
      Wilson, C. T. Design considerations for next-generation sorbent-based atmospheric water-harvesting devices. Device 2023, 1, 100052,  DOI: 10.1016/j.device.2023.100052
      There is no corresponding record for this reference.
    26. 26
      Min, X. High-Yield Atmospheric Water Harvesting Device with Integrated Heating/Cooling Enabled by Thermally Tailored Hydrogel Sorbent. ACS Energy Lett. 2023, 8, 3147– 3153,  DOI: 10.1021/acsenergylett.3c00682
      26
      High-Yield Atmospheric Water Harvesting Device with Integrated Heating/Cooling Enabled by Thermally Tailored Hydrogel Sorbent
      Min, Xinzhe; Wu, Zhen; Wei, Tianqi; Hu, Xiaozhen; Shi, Peiru; Xu, Ning; Wang, Haiming; Li, Jinlei; Zhu, Bin; Zhu, Jia
      ACS Energy Letters (2023), 8 (7), 3147-3153CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      Sorption-based atm. water harvesting (AWH) is regarded as a promising way to produce fresh water in water-stressed areas. However, low water prodn. per unit device mass (WPD) and high energy consumption restrict its applications in portable fresh water replenishment. Here we report a portable high-yield AWH device based on a thermoelec. cell (TEC)-driven integrated heating/cooling thermal design, enabled by a thermally tailored hydrogel sorbent. Heat and cold energies for desorption and condensation are simultaneously generated by the TEC. Graphene oxide-doped sodium alginate hydrogel with high thermal cond. is tailored as the sorbent, which tightly adheres to the TEC's hot region and efficiently takes heat away, for fast desorption as well as temp. control of the TEC. Based on the thermal design of the device and materials, a total WPD of 0.18 L kgdevice-1 h-1 is achieved under 80% RH, almost an order of magnitude higher than that of the traditional design with the same energy input.
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    27. 27
      Li, R.; Shi, Y.; Wu, M.; Hong, S.; Wang, P. Improving atmospheric water production yield: Enabling multiple water harvesting cycles with nano sorbent. Nano Energy 2020, 67, 104255,  DOI: 10.1016/j.nanoen.2019.104255
      27
      Improving atmospheric water production yield: Enabling multiple water harvesting cycles with nano sorbent
      Li, Renyuan; Shi, Yusuf; Wu, Mengchun; Hong, Seunghyun; Wang, Peng
      Nano Energy (2020), 67 (), 104255CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)
      Clean water shortage has long been a challenge in remote and landlocked communities esp. for the impoverished. Atm. water is now considered as an unconventional but accessible fresh water source and sorption-based atm. water generator (AWG) has been successfully demonstrated a reliable way of harvesting atm. water. The water vapor sorbents with high water uptake capacity and esp. fast vapor sorption/desorption kinetics have become the bottleneck to a desirable clean water productivity in AWG. In this work, we developed a new nano vapor sorbent composed of a nano carbon hollow capsule with LiCl inside the void core. The sorbent can capture water vapor from ambient air as much as 100% of its own wt. under RH 60% within 3 h and quickly release the sorbed water within just half hour under 1 kW/m2 sunlight irradn. A batch-mode AWG device was able to conduct 3 sorption/desorption cycles within 10 h during one day test in the outdoor condition and produced 1.6 kgwater/kgsorbent. A prototype of continuous AWG device was designed, fabricated, and successfully demonstrated, hinting a possible way of large-scale deployment of AWG for practical purposes.
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    28. 28
      Kim, H.; Rao, S. R.; LaPotin, A.; Lee, S.; Wang, E. N. Thermodynamic analysis and optimization of adsorption-based atmospheric water harvesting. Int. J. Heat Mass Transf 2020, 161, 120253,  DOI: 10.1016/j.ijheatmasstransfer.2020.120253
      There is no corresponding record for this reference.
    29. 29
      Li, A. C. Thermodynamic limits of atmospheric water harvesting with temperature-dependent adsorption. Appl. Phys. Lett. 2022, 121, 164102,  DOI: 10.1063/5.0118094
      There is no corresponding record for this reference.
    30. 30
      Kayal, S.; Baichuan, S.; Saha, B. B. Adsorption characteristics of AQSOA zeolites and water for adsorption chillers. Int. J. Heat Mass Transf 2016, 92, 1120– 1127,  DOI: 10.1016/j.ijheatmasstransfer.2015.09.060
      There is no corresponding record for this reference.
    31. 31
      Zhou, X.; Lu, H.; Zhao, F.; Yu, G. Atmospheric Water Harvesting: A Review of Material and Structural Designs. ACS Mater. Lett. 2020, 2, 671– 684,  DOI: 10.1021/acsmaterialslett.0c00130
      31
      Atmospheric Water Harvesting: A Review of Material and Structural Designs
      Zhou, Xingyi; Lu, Hengyi; Zhao, Fei; Yu, Guihua
      ACS Materials Letters (2020), 2 (7), 671-684CODEN: AMLCEF; ISSN:2639-4979. (American Chemical Society)
      A review. Atm. water harvesting (AWH) emerges as a promising means to overcome the water scarcity of arid regions, esp. for inland areas lacking liq. water sources. Beyond conventional system engineering that improves the water yield, novel moisture-harvesting materials provide new aspects to fundamentally promote the AWH technol. benefiting from their high tunability and processability. Innovative material and structural designs enable the moisture harvesters with desirable features, such as high water uptake, facile water collection and long-term recyclability, boosting the rapid development of next-generation AWH. In this Perspective, we first illustrate the sorption mechanism, including absorption and adsorption for moisture-harvesting materials and summarize fundamental requirements, as well as design principles of moisture harvesters. Recent progress on material and structural designs of moisture harvesters for AWH is critically discussed. We conclude with prospective directions for next-generation moisture harvesters to promote AWH from scientific research to practical application.
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    32. 32
      LaPotin, A.; Kim, H.; Rao, S. R.; Wang, E. N. Adsorption-Based Atmospheric Water Harvesting: Impact of Material and Component Properties on System-Level Performance. Acc. Chem. Res. 2019, 52, 1588– 1597,  DOI: 10.1021/acs.accounts.9b00062
      32
      Adsorption-Based Atmospheric Water Harvesting: Impact of Material and Component Properties on System-Level Performance
      LaPotin, Alina; Kim, Hyunho; Rao, Sameer R.; Wang, Evelyn N.
      Accounts of Chemical Research (2019), 52 (6), 1588-1597CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      Atm. H2O harvesting (AWH) is the capture and collection of H2O that is present in the air either as vapor or small H2O droplets. AWH has been recognized as a method for decentralized H2O prodn., esp. in areas where liq. H2O is phys. scarce, or the infrastructure required to bring H2O from other locations is unreliable or infeasible. The main methods of AWH are fog harvesting, dewing, and using sorbent materials to collect vapor from the air. We 1st distinguish between the geog./climatic operating regimes of fog harvesting, dewing, and sorbent-based approaches based on temp. and relative humidity (RH). Because using sorbents has the potential to be more widely applicable to areas which are also facing H2O scarcity, we focus the discussion on this approach. We discuss sorbent materials which have been developed for AWH and the material properties which affect system-level performance. Much of the recent materials development has focused on a single material metric, equil. vapor uptake in (kg of H2O uptake per kg of dry adsorbent), as found from the adsorption isotherm. This equil. property alone, however, is not a good indicator of the actual performance of the AWH system. Understanding material properties which affect heat and mass transport are equally important in the development of materials and components for AWH, because resistances assocd. with heat and mass transport in the bulk material dramatically change the system performance. We focus the discussion on modeling a solar thermal-driven system. Performance of a solar-driven AWH system can be characterized by different metrics, including L of H2O per m2 device per day or L of H2O per kg adsorbent per day. The former metric is esp. important for systems driven by low-grade heat sources because the low power d. of these sources makes this technol. land area intensive. In either case, it is important to include rates in the performance metric to capture the effects of heat and mass transport in the system. We discuss the previously developed modeling framework which can predict the performance of a sorbent material packed into a porous matrix. This model connects mass transport across length scales, considering diffusion both inside a single crystal as well as macroscale geometric parameters, such as the thickness of a composite adsorbent layer. For a simple solar thermal-driven adsorption-based AWH system, we show how this model can be used to optimize the system. Finally, we discuss strategies which have been used to improve heat and mass transport in the design of adsorption systems and the potential for adsorption-based AWH systems for decentralized H2O supplies.
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    33. 33
      El Fil, B.; Li, X.; Díaz-Marín, C. D.; Zhang, L.; Jacobucci, C. L. Significant enhancement of sorption kinetics via boiling-assisted channel templating. Cell Rep. Phys. Sci. 2023, 4, 101549,  DOI: 10.1016/j.xcrp.2023.101549
      There is no corresponding record for this reference.

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