Hydrogen Storage in Crystalline and Amorphous High‐Entropy Alloys: Linking Absorption/Desorption Kinetics to Structural–Morphological–Compositional Evolution

ABSTRACT

This study examines the hydrogen storage behavior in amorphous high‐entropy alloys (HEA), aiming to address the limited understanding of poorly crystalline systems compared to their crystalline counterparts, with emphasis on absorption/desorption kinetics and structural, morphological, and compositional evolution during hydrogenation–dehydrogenation cycling. Neutron techniques including neutron powder diffraction (NPD) and small‐angle neutron scattering (SANS) were employed to probe structural and morphological changes. The amorphous HEA exhibits a disordered atomic structure, which enables faster hydrogen transport and lower apparent activation energies than crystalline HEA, where diffusion is hindered by phase and grain boundary barriers. However, hydrogenation–dehydrogenation induces elemental redistribution and a progressive disorder‐to‐order transition leading to the formation and growth of local ordered regions and eventual crystallization in the amorphous alloy, as confirmed by SANS. In contrast, crystalline HEA undergoes significant pulverization, particularly during dehydrogenation associated with phase mismatch and stress accumulation. These results demonstrate that although amorphous HEA offers enhanced absorption kinetics, the structural instability represents a key limitation. The interplay between the atomic arrangement, absorption/desorption behavior, structural, morphological, and compositional evolution provides insight into the design of HEA with amorphous structure for hydrogen storage applications.