A focused mini-review on high-entropy intermetallics for hydrogen storage

Intermetallic compounds (IMCs) are considered desirable materials for hydrogen storage. However, traditional hydrogen-storage IMCs have many shortcomings. High-entropy alloys (HEAs), which are composed of multiple metallic elements, exhibit significant lattice distortion and large interstitial sites, making them a promising class of hydrogen storage materials. Among the HEAs used for hydrogen storage, high-entropy intermetallics (HEIs) have shown great potential for hydrogen absorption kinetics and cycling stability, particularly for room-temperature hydrogen storage. This review systematically summarizes research progress on HEIs for hydrogen storage. It first presents a statistical analysis of composition design methods for these alloys, including empirical criteria based on parameters such as valence electron concentration and atomic size mismatch, as well as thermodynamic calculations such as the calculated phase diagram (CALPHAD) method. It then summarizes the characteristics and hydrogen storage performance of the reported alloys, with a detailed discussion of their phase compositions, microstructures, and the corresponding effects on hydrogen storage properties. Particular emphasis is placed on the critical roles of phase boundaries, multiphase synergy, and specific microstructural features (e.g., networked/eutectic morphologies) in enhancing activation performance and improving hydrogen diffusion kinetics. Although the current hydrogen storage capacity of HEIs (approximately 1 H/M (hydrogen-to-metal atomic ratio)) remains lower than that of BCC-structured HEAs, their exceptional reversible hydrogen absorption/desorption capability at room temperature, lack of activation requirements, and remarkable cycling stability make them highly promising for applications in which a moderate capacity is sufficient, such as mobile hydrogen storage. This review provides a systematic summary of research progress on HEIs for hydrogen storage, focusing on the effects of alloy design strategies, phase composition, and microstructural regulation on hydrogen storage properties. The primary challenge currently facing HEIs is their relatively low hydrogen storage capacity. Accordingly, this paper outlines future development directions to address this issue. This review provides a theoretical basis and guidance for the development of next-generation high-performance hydrogen storage materials.