Recent advances in hydrogen storage properties of high-entropy alloys: from alloy design to performance

Abstract

High- and medium-entropy alloys (HEAs/MEAs) have emerged as tunable platforms for solid-state hydrogen storage because they enable simultaneous control of phase constitution, hydrogen thermodynamics, and microstructure across a broad compositional space. This review summarizes recent advances in alloy design, processing, and hydrogen storage performance, with an emphasis on how electronic and geometric descriptors, combined with thermodynamic screening, can be used to identify hydrogen-relevant phases. Two major alloy families are discussed. C14 Laves phase HEAs generally exhibit faster sorption kinetics, easier activation, and more suitable operation near room temperature, although their hydrogen capacities are typically moderate. In contrast, refractory BCC-based HEAs often provide higher hydrogen uptake, but they commonly face challenges related to hydride over-stability, elevated desorption temperatures, hysteresis, and limited reversibility. Beyond alloy composition, this review examines how processing routes, particularly mechanical alloying and severe plastic deformation, modify defect structures and interface density, thereby influencing activation behavior, sorption kinetics, and cycling stability. The mechanisms associated with hysteresis and capacity degradation are also critically discussed, especially those related to phase transformations, chemical heterogeneity, and defect-mediated hydrogen trapping. Finally, the review highlights the main remaining challenges and future perspectives, including application-oriented benchmarking, improved standardization of testing protocols, and the increasing integration of CALPHAD, density functional theory (DFT), and data-driven approaches to accelerate the design of hydrogen storage alloys with practical reversible capacity and long-term stability.