In this paper we present amorphous chromium(III) hydride gels that show promise as reversible room temperature hydrogen storage materials with potential for exploitation in mobile applications. The material uses hydride ligands as a light weight structural feature to link chromium(III) metal centres together which act as binding sites for further dihydrogen molecules via the Kubas interaction, the mode of hydrogen binding confirmed by high pressure Raman spectroscopy. The best material possesses a reversible gravimetric storage of 5.08 wt% at 160 bar and 25 °C while the volumetric density of 78 kgH2 m(-3) compares favourably to the DOE ultimate system goal of 70 kg m(-3). The enthalpy of hydrogen adsorption is +0.37 kJ mol(-1) H2 as measured directly at 40 °C using an isothermal calorimeter coupled directly to a Sieverts gas sorption apparatus. These data support a mechanism confirmed by computations in which the deformation enthalpy required to open up binding sites is almost exactly equal and opposite to the enthalpy of hydrogen binding to the Kubas sites, and suggests that this material can be used in on-board applications without a heat management system.

An amorphous manganese hydride molecular sieve that reversibly absorbs 10.5 wt% and 197 kgH2 m−3 hydrogen at room temperature using the Kubas interaction.

Manganese(II) hydrazide gels designed for Kubas-type hydrogen storage were synthesized from the reaction between bis(trimethylsilylmethyl) manganese and anhydrous hydrazine. The synthetic materials were characterized by X-ray powder diffraction, nitrogen adsorption, X-ray photoelectron spectroscopy, infrared spectroscopy, and elemental analysis. Hydrogen storage measurements were conducted on materials with hydrazine:Mn ratios of 0.5:1, 1:1. 1.5:1, and 2:1. The best results were obtained with the 1:1 material, which demonstrated as high as 1.01 wt % and 32 kg/m 3 at 77 K and 85 bar and 1.06 wt % and 24.2 kg/ m 3 at 298 K at 85 bar. Measurements up to 143 bar at 298 K led to an adsorption value of 1.65 wt % and 37.7 kg/m 3 without saturation. The isosteric enthalpy of this material rose with surface coverage from 1.3 to 39 kJ/mol. Excess void space was removed from the materials by compressing at 500 Psi and the resulting compressed gel pellets possess an absolute volumetric adsorption of 18.97 kg/m 3 at 298 K and 85 bar. The mechanism of hydrogen storage was probed with electron paramagnetic resonance (EPR), which showed signal enhancements when sample was held under 1 bar hydrogen, both at room temperature and at 77 K. This was interpreted as a perturbation due to hydrogen binding to the Mn center.

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 solidstate 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 TiH 5 and TiH 7 species, in some ways analogous to hypervalent MH 5 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/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.