Observation of TiH₅ and TiH₇ in bulk-phase TiH ₃ 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 H₂ 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 H₂ chemisorption. High-pressure Raman spectroscopy confirmed the first evidence of TiH₅ and TiH₇ species, in some ways analogous to hypervalent MH₅ and MH ₇ (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/m³, comparable to the DOE 2017 volumetric system goal of 40 kgH₂/m ³. However, extrapolations show that the phase-pure material is capable of binding at least 6 wt % hydrogen reversibly at room temperature.