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

• Alloys of non-equiatomic Ti-V-Nb-Cr-Al systems for hydrogen absorption storage were designed theoretically via HEAPS, CALPHAD, and PCT code. • Both the VEC and δr parameters rises with the Nb/Cr/Al content, signifying rise in lattice distortion for increase in gravimetric capacity. • Maximum hydrogen absorption capacity of the Nb-based alloy reaches 3.68wt.% with plateau pressure to ∼1 bar at room temperature condition in the Ti 24 V 24 Nb 20 Cr 16 Al 16 alloy. • A single-phase SS BCC structure was obtained predominantly for all the combination of different proportion of non-equiatomic TiVNbCrAl-based alloys. 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)—Ti 33 V 33 Nb 14 Cr 10 Al 10 , Ti 30 V 30 Nb 16 Cr 12 Al 12 , Ti 27 V 27 Nb 18 Cr 14 Al 14 and Ti 24 V 24 Nb 20 Cr 16 Al 16 —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 Ti 24 V 24 Nb 20 Cr 16 Al 16 . Gravimetric capacity indicated a steady, marginal variations 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 Nb content, and thereby offers guidance for the design of novel LWRHEAs for advanced hydrogen storage applications.