Observation of TiH5 and TiH7 in Bulk-Phase TiH3 Gels for Kubas-Type Hydrogen Storage

The lack of an efficient hydrogen storage material has so far hindered the implementation of hydrogen as an energy vector, that is, a substance that allows the transfer through space and time of a certain quantity of energy from its original source. This work presents porous Ti(III) hydride gels as a promising new hydrogen storage material, exploiting the first example of a solid-state homoleptic metal hydride that binds further H-2 ligands using the Kubas interaction. These materials use bridging hydride ligands as an ultralightweight structural feature to support a microporous network of Ti binding sites for molecular H-2 chemisorption. High-pressure Raman spectroscopy confirmed the first evidence of TiH5 and TiH7 species, in some ways analogous to hypervalent MH5 and MH7 (M = Si, Ge, Sn) species. The material with the highest capacity has an excess reversible storage of 3.49 wt % at 140 bar and 298 K without saturation, corresponding to a volumetric density of 44.3 kg/m(3), comparable to the DOE 2017 volumetric system goal of 40 kgH(2)/m(3). However, extrapolations show that the phase-pure material is capable of binding at least 6 wt % hydrogen reversibly at room temperature.