Synthesis and Electrochemical Evaluation of Multivalent Vanadium Hydride Gels for Lithium and Hydrogen Storage

A vanadium aryl hydride gel was prepared by thermal decomposition and subsequent hydrogenation of tetraphenyl vanadium and evaluated for electrochemical and hydrogen storage performance. Characterization by IR, XRD, XPS, nitrogen adsorption, and TGA suggests that the material consists predominantly of a mixture of vanadium centers in oxidation states of II-IV bound together by bridging hydride and phenyl groups. Electrochemical properties were explored to probe the reversible oxidation state behavior and possible applications to Li batteries, with the hypothesis that the low mass of the hydride ligand may lead to superior gravimetric performance relative to heavier vanadium oxides and phosphates. The material shows reversible redox activity and has a promising peak capacity of 131 mAh g^-1, at a discharge rate of 1 mA cm^-2, comparable to bulk VO₂ samples also tested in this study. After repeated charge-discharge cycling for 50 cycles, the material retained 36% of its capacity. The material also shows improved hydrogen storage performance relative to previously synthesized VH₃ based gels, reaching a reversible gravimetric storage capacity of 5.8 wt % at 130 bar and 25 °C. Based on the measured density, this corresponds to a volumetric capacity of 79.77 kg H₂ m^-3, demonstrating that the 2017 U.S. DOE system goals of 5.5 wt % and 40 kg H₂ m^-3 may be achievable upon containment in a Type 1 tank and coupling to a fuel cell.