Catalytic role of TiNiAlZn medium-entropy alloy in mg-based hydrogen storage: microstructure, kinetics, and mechanism

Abstract Magnesium is a promising hydrogen storage material due to its high gravimetric hydrogen capacity; however, its practical application is limited by slow sorption kinetics and high activation energies. In this study, a TiNiAlZn medium-entropy alloy (MEA) was designed and synthesized via mechanical alloying as a catalytic additive to enhance the hydrogen storage performance of Mg. An equiatomic face-centered cubic (FCC)-structured TiNiAlZn MEA was successfully synthesized after 15 h of mechanical alloying and uniformly incorporated into Mg at 0, 3, 6, and 9 wt.%. Hydrogen absorption–desorption measurements performed at 325, 350, and 375 °C under 4 MPa H 2 demonstrate that MEA addition markedly accelerates hydrogen sorption kinetics while maintaining a high reversible hydrogen capacity. Among the investigated compositions, Mg–6 wt.% MEA exhibits the best overall performance, achieving rapid hydrogen absorption (∼6.5 wt.%) and near-complete desorption within minutes. Kinetic analysis using the Johnson–Mehl–Avrami–Kolmogorov model suggests diffusion- and interface-controlled reaction mechanisms. Arrhenius analysis reveals that the apparent absorption activation energy decreases from 64.00 kJ·mol −1 for pure Mg to 30.46 kJ·mol −1 for Mg–6 wt.% MEA, while the desorption activation energy decreases from 188.89–125.42 kJ·mol −1 . Microstructural and phase analyses confirm the formation of a stable FCC MEA phase, homogeneous dispersion within the Mg matrix, and the presence of extensive Mg–MEA interfacial contact. The improved hydrogen sorption behavior is attributed to the combined effects of the structurally stable FCC MEA phase, increased Mg–MEA interfacial area, and sub-micron, defect-rich Mg microstructure generated during mechanical alloying. Excessive MEA loading (9 wt.%) promotes particle coarsening, reducing the effective interfacial area and partially offsetting the catalytic benefits. These findings demonstrate that medium-entropy alloy catalysts provide an effective strategy for tailoring interfacial characteristics and reducing kinetic barriers in Mg-based solid-state hydrogen storage systems.