Tuning the hydrogen storage properties of MOF-650: A combined DFT and GCMC simulations study

Abstract

Combined density functional theory and grand canonical monte Carlo (GCMC) calculations were performed to study the electronic structures and hydrogen adsorption properties of the Zn-based metal-organic framework MOF-650. The benzene azulenedicarboxylate linkers of MOF-650 were substituted by B atoms, N atoms, and boronic acid B(OH)2 linkers, and the Zn atoms were substituted by Mg and Ca atoms. The calculated electronic densities of states (DOSs) of MOF-650 showed that introduction of B atoms reduces the band gap but damages the structure of MOF-650. Introduction of single N bonds cannot provide active electrons to attract H2 molecules. Thus, substitutions of B and N into MOF-650 are not suggested. B(OH)2 substitute in MOF-650 decreased its band gap, slightly improved its hydrogen storage ability and made H2 molecules more intensively distributed besides organic linkers. GCMC calculations were carried out by estimating the H2 storage amount of the pure and modified MOFs at 77 and 298 K and from 1 bar to 20 bar. B(OH)2 linker and Mg/Ca co-doped MOF-650 showed increased H2 adsorption by approximately 20 wt%. The adsorption of H2 around different bonds showed the order N–C < C = C < B–C < C–O < B–O.