Thermodynamic modeling of non-equiatomic TiVNbCrAl-based lightweight refractory high-entropy alloys (LWRHEAs) for hydrogen storage applications

Abstract

Hydrogen, as a clean alternative energy carrier, is a key element in the global energy transition with great potential to significantly reduce the carbon footprint of transportation and other sectors. In this context, high-entropy alloys (HEAs) have emerged as promising candidates for hydrogen storage. Among them, refractory body-centered cubic (BCC)-based HEAs have demonstrated exceptional storage properties, achieving hydrogen-to-metal ratios up to 2.0 H/M, which motivates research into novel systems under moderate conditions. However, their practical application is hindered by thermodynamic and kinetic limitations, such as low-pressure conditions, difficult activation, high hydride stabilities, and consequently, high desorption temperatures. In this study, four lightweight refractory HEAs (LWRHEAs)—Ti₃₃V₃₃Nb₁₄Cr₁₀Al₁₀, Ti₃₀V₃₀Nb₁₆Cr₁₂Al₁₂, Ti₂₇V₂₇Nb₁₈Cr₁₄Al₁₄ and Ti₂₄V₂₄Nb₂₀Cr₁₆Al₁₆—were selected from eight candidates that satisfied empirical phase criteria and were predicted to form a single BCC solid solution; their hydrogen-storage properties were then systematically characterized. Pressure-composition-temperature (PCT) curves revealed an unusually high hydrogen uptake of ∼2.0 H/M at 25 and 100 °C. The equilibrium plateau pressure increased steadily with composition, reaching nearly 1 bar for Ti₂₄V₂₄Nb₂₀Cr₁₆Al₁₆. Gravimetric capacity indicated a small, marginal variation with Nb/Cr/Al additions ranging from 3.60 to 3.68 wt% as the valence electron concentration (VEC) value increases, showing a remarkable capacity not commonly reported in BCC-based alloys. This study provides important insights into the compositional tuning of TiV-based BCC HEAs, demonstrating the effective synergy of Al/Cr additions with increased niobium (Nb) content, and thereby offers guidance for the design of novel LWRHEAs for advanced hydrogen storage applications.