MOF-5 composites exhibiting improved thermal conductivity

The low thermal conductivity of the prototype hydrogen storage adsorbent, metal-organic framework 5 (MOF-5), can limit performance in applications requiring rapid gas uptake and release, such as in hydrogen storage for fuel cell vehicles. As a means to improve thermal conductivity, we have synthesized MOF-5-based composites containing 1-10 wt.% of expanded natural graphite (ENG) and evaluated their properties. Cylindrical pellets of neat MOF-5 and MOF-5/ENG composites with densities of 0.3, 0.5, and 0.7 g/cm(3) are prepared and assessed with regard to thermal conductivity, specific heat capacity, surface area, and crystallinity. For pellets of density 0.5 g/cm(3), we find that ENG additions of 10 wt.% result in a factor of five improvement in thermal conductivity relative to neat MOF-5, increasing from 0.10 to 0.56 W/mK at room temperature. Based on the relatively higher densities, surface areas, and enhanced crystallinity exhibited by the composites, ENG additions appear to partially protect MOF-5 crystallites from plastic deformation and/or amorphization during mechanical compaction; this suggests that thermal conductivity can be improved while maintaining the favorable hydrogen storage properties of this material. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.