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

Abstract

ABSTRACT: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 mAhg -1 , at a discharge rate of 1 mAcm -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 kgH2 m -3 , demonstrating that the 2017 US 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.

A manganese hydride molecular sieve for practical hydrogen storage under ambient conditions

“…3D) are endothermic and do not increase or decrease significantly with increased surface coverage. This supports the mechanism discussed at length previously and supported by computations and high-pressure Raman measurements [15][16][17] in which the 20-40 kJ mol À1 H 2 energy expected for Kubas binding of hydrogen 8,9 is offset by twisting of the material as the pressure increases to open up new binding sites. 26 A MOF has been reported that undergoes structural deformation on application of pressure and this deformation influences the adsorption properties.…”

“…This method of synthesizing a solid-state transition metal hydride from a metal alkyl has been reported previously by our group for Ti, Cr, and V systems. [14][15][16][17] The resulting black air sensitive solid (KMH-1 as synthesized) still contained hydrocarbon as evidenced by the infrared (IR) spectrum ( Fig. S1, ESI †) and because of this was hydrogenated in the solid state at 373 K and 85 bar for 4 hours to give KMH-1 after 1st hydrogenation.…”

“…This is also true for other transition-metal alkyl hydride materials previously reported by our group. [14][15][16][17] The Energy Dispersive X-ray Spectroscopy (EDS) for KMH-1 as synthesized ( Fig. S12 and Table S2, ESI †) and KMH-1 after 2nd hydrogenation ( Fig.…”

“…28 Furthermore, while it is difficult to directly compare batteries and fuel cells, using an estimated price of 50 $ per kW for mass production of fuel cells, 29 the complete fuel cell energy storage system projects as roughly 3-4 times less expensive than the current price of about 200 $ per kW h for lithium batteries. 10 While high-pressure Raman measurements were used to confirm Kubas binding in closely analogous V, Cr, and Ti materials studied previously by our group, [14][15][16][17] inelastic neutron scattering (INS) is a generally considered to be a more informative technique to explore hydrogen binding. Thus, to probe the mechanism of hydrogen binding more deeply, INS studies were performed on a sample of KMH-1 after 2nd hydrogenation; the results are shown in Fig.…”

Computational study of H2 binding to MH3 (M = Ti, V, or Cr)

“…In recent years there has been an increasing interest in developing materials that exploit the Kubas interaction including, from our labs, those based on hydrazines 20 , hydrazides 21 , doped mesoporous silica molecular sieves 22,23 , and early transition metal alkyl hydride gels [24][25][26][27] . The latter have shown considerable promise as novel hydrogen storage materials;…”