A comprehensive investigation of the (Ti0.5Zr0.5)1(Fe0.33Mn0.33Cr0.33)2 multicomponent alloy for room-temperature hydrogen storage designed by computational thermodynamic tools

Multicomponent alloys with C14 Laves phase structures are promising hydrogen storage materials because of their ability to reversibly absorb substantial amounts of hydrogen at room temperature with good kinetics, long cycling life, and easy activation. The applicability of these alloys as hydrogen storage media is governed by their thermodynamic properties, which can be tuned by the design of the chemical composition, as well as electronic and geometrical factors. In this work, the (Ti0.5Zr0.5)(1)(Fe0.33Mn0.33Cr0.33)(2) alloy was designed using computational thermodynamic tools. CALPHAD calculation predicted that this alloy would solidify as a single C14 Laves phase. Moreover, the calculation of the pressure-composition-temperature (PCT) diagram, using a recently developed thermodynamic model, indicated that it would present mild hydrogen equilibrium pressure (similar to 12 bar) at room temperature. The calculated hydrogen equilibrium pressure in the order of 10(1) bar would enable this alloy to store hydrogen at room temperature reversibly. The alloy was synthesized by arc-melting, and X-ray powder diffraction (XRD) demonstrated that the alloy indeed solidified as a single C14 Laves phase. The thermodynamic properties of the alloy during the hydrogen absorption and desorption processes were experimentally investigated by the acquisition of PCT diagrams. The alloy absorbs at room temperature a large amount of hydrogen (up to 1 H/M; similar to 1.7 wt%) under moderate hydrogen equilibrium pressures and with fast kinetics. Furthermore, it was demonstrated that the alloy reversibly absorbs and desorbs the total amount of hydrogen (H/M = 1) at room temperature with excellent cycling stability.