High capacity hydrogen storage in closo-hexaborate dianion B6H62−

The capacity of LimB6H62− (m = 1, 2) as a hydrogen storage medium is studied using density functional theory. The binding strength of Li atom is sufficiently large to ensure the stability of LimB6H62−. Each Li atom can adsorb six H2 molecules and the B6H6 moiety can adsorb four H2 molecules. Li2B6H62− can bind up to 16 H2 molecules with an average binding energy of 0.169 eV/H2, leading to a hydrogen storage capacity of 27.1 wt%, which is much higher than that of the neutral Li2B6H6 system. The enhanced electrostatic field around the Li atom originates from the charge transfer from B6H62− to Li, accounting for the high adsorption capacity. The electrostatic field can be enhanced by controlling the charge state of the metal–organic complex, thereby significantly improving the hydrogen adsorption capacity.