Hydrogen Storage Properties of a New Ti-V-Cr-Zr-Nb High Entropy Alloy

Abstract

We are reporting the synthesis, the physicochemical, and the hydrogen sorption properties of a novel bcc high entropy alloy Ti0.30V0.25Cr0.10Zr0.10Nb0.25. At room temperature, the alloy rapidly absorbs hydrogen reaching a capacity of 2.0 H/M (3.0 wt.%) and forming a dihydride with fcc structure, as confirmed by both synchrotron X-ray diffraction and neutron diffraction. The absorption Pressure–Composition Isotherms corroborated with synchrotron X-ray diffraction prove that the reaction with hydrogen occurs within two steps, i.e., bcc alloy → bcc monohydride → fcc dihydride. The thermodynamic parameters calculated for the second step transformation evidence the formation of a stable dihydride with ΔHabs = −75 kJ/molH2. The phase transition during hydrogen/deuterium desorption was investigated by in situ synchrotron X-ray and neutron diffraction confirming a reversible reaction with hydrogen. Furthermore, the cycling properties show a decrease of the capacity over the first cycles followed by a stabilization at 2.44 wt.%, whereas the absorption kinetics improve after the first cycle reaching full capacity after only 30 s at room temperature.