Theoretical assessment of the elastic constants and hydrogen storage capacity of some metal-organic framework materials

Metal-organic frameworks (MOFs) are promising materials for applications such as separation, catalysis, and gas storage. A key indicator of their structural stability is the shear modulus. By density functional theory calculations in a 106-atom supercell, under the local density approximation, we find c 11 = 29.2 GPa and c 12 = 13.1 GPa for Zn-based MOF 5. However, we find c 44 of MOF-5 to be exceedingly small, only 1.4 GPa at T = 0 K . The binding energy E ads of a single hydrogen molecule in MOF-5 is evaluated using the same setup. We find it to be − 0.069 to − 0.086 eV ∕ H 2 near the benzene linker and − 0.106 to − 0.160 eV ∕ H 2 near the Zn 4 O tetrahedra. Substitutions of chlorine and hydroxyl in the benzene linker have negligible effect on the physisorption energies. Pentacoordinated copper (and aluminum) in a framework structure similar to MOF-2 gives E ads ≈ − 0.291 eV ∕ H 2 (and − 0.230 eV ∕ H 2 ), and substitution of nitrogen in benzene (pyrazine) further enhances E ads near the organic linker to − 0.16 eV ∕ H 2 , according to density functional theory with local density approximation.