A Predictive Model of Hydrogen Sorption for Metal-Organic Materials

Newly developed hydrogen and MOM (Metal-Organic Materials) potential energy functions for molecular simulation are presented. They are designed to be highly transferable while still describing sorbate-MOM interactions with predictive accuracy. Specifically, they are shown to quantitatively describe hydrogen sorption, including isosteric heats, in MOF-5 over the broad temperature and pressure ranges that have been examined experimentally. The approach that is adopted is general and demonstrates that highly accurate and predictive models of molecular interaction with MOMs are quite feasible. Molecular interactions giving rise to the isosteric heat have been characterized and validated against the experimentally relevant data. Finally, inspection of the isothermal compressibility of hydrogen in MOF-5 reveals that under saturating high-pressure conditions (even at temperatures well above the neat boiling point) the state of hydrogen is characteristic of a liquid, i.e., with a compressibility similar to that of bulk hydrogen. This result is of particular relevance in developing MOMs for hydrogen-storage applications.