Increasing the Density of Adsorbed Hydrogen with Coordinatively Unsaturated Metal Centers in Metal−Organic Frameworks

Yun Liu,†‡ Houria Kabbour,§ Craig M. Brown,† Dan A. Neumann,† and Channing C. Ahn*§
NIST Center for Neutron Research, National Institute of Standards and Technology, Maryland, Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, and Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California
Langmuir, 2008, 24 (9), pp 4772–4777
DOI: 10.1021/la703864a
Publication Date (Web): March 27, 2008
Copyright © 2008 American Chemical Society
†

 National Institute of Standards and Technology.

,
‡

 University of Maryland.

,
§

 California Institute of Technology.

,
*

 Corresponding author. E-mail:  cca@caltech.edu.

Abstract

Abstract Image

Storing molecular hydrogen in porous media is one of the promising avenues for mobile hydrogen storage. In order to achieve technologically relevant levels of gravimetric density, the density of adsorbed H2 must be increased beyond levels attained for typical high surface area carbons. Here, we demonstrate a strong correlation between exposed and coordinatively unsaturated metal centers and enhanced hydrogen surface density in many framework structures. We show that the MOF-74 framework structure with open Zn2+ sites displays the highest surface density for physisorbed hydrogen in framework structures. Isotherm and neutron scattering methods are used to elucidate the strength of the guest−host interactions and atomic-scale bonding of hydrogen in this material. As a metric with which to compare adsorption density with other materials, we define a surface packing density and model the strength of the H2-surface interaction required to decrease the H2−H2 distance and to estimate the largest possible surface packing density based on surface physisorption methods.

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History

  • Published In Issue May 06, 2008
  • Received December 11, 2007
    Revised February 5, 2008

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