Experimental and Theoretical Investigation Into Hydrogen Storage via Spillover in IRMOF-8

The principal obstacle to the implementation of a hydrogen-based economy remains storage under ambient conditions of temperature and pressure. While most approaches to this problem have to date focused on physisorption, wherein useful uptake is realized only at low temperatures (e.g., 77 K), recent experiments have suggested the possibility of chemisorptive strategies based on hydrogen spillover. We report the results of an experimental and a theoretical investigation into the thermochemistry of dihydrogen chemisorption on a catalytically activated isoreticular metal organic framework (IRMOF). Experimental results demonstrate a spillover mechanism leading to 2.5 wt % uptake at 75 bar for Pt-catalyzed, carbon-bridged IRMOF-8 [Zn₄O(naphthalene-2,6-dicarboxylate)₃], while theoretical results suggest the thermochemical plausibility of this mechanism and offer upper limits for chemisorption in these materials. Laser thermal-desorption mass spectrometry measurements further reveal multiple binding sites occurring between 263 and 298 K, substantially higher than that for simple physisorbed dihydrogen (165 K) and consistent with the reported isosteric enthalpies based upon theoretical partition functions for the chemisorbed structures.