Abstract
•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 Ti24V24Nb20Cr16Al16 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)—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 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.