Improvement of dehydrogenation kinetics of MgH2 with VMnFeCoNi high-entropy alloy

Among solid hydrogen storage materials, MgH₂ possesses abundant resources, low cost, and a high hydrogen storage capacity. Nonetheless, its elevated hydrogen desorption temperature and sluggish hydrogen desorption kinetics constrain its practical application. This study presents the preparation of a low-cost VMnFeCoNi single-phase high-entropy alloy using mechanical ball milling and powder metallurgy to reduce the hydrogen absorption and desorption temperature of MgH₂ to enhance its dehydrogenation kinetics. The findings indicate that incorporating high-entropy alloy VMnFeCoNi into MgH₂ markedly lowers the dehydrogenation temperature, enhances the dehydrogenation rate, and diminishes the dehydrogenation activation energy of MgH₂. Utilising XRD, TEM, and SEM analyses of the microstructure, the VMnFeCoNi nanoparticles synthesised via wet ball milling are uniformly dispersed across the MgH₂ matrix surface, offering numerous active sites for MgH₂. The transition metal elements significantly attract hydrogen atoms and enhance hydrogen desorption on the surface of MgH₂ by including 5 wt%. The initial dehydrogenation temperature of MgH₂ is 493 K, with the activation energy for dehydrogenation decreasing from 154.60 kJ/mol H₂ to 93.67 kJ/mol H₂, and hydrogen absorption can occur at 473 K and 3.5 MPa hydrogen pressure. The hydrogen absorption capacity attains 5.651 wt%. The saturated hydrogen absorption capacity is 6.144 wt% at 613 K and 3.5 MPa hydrogen pressure, achieving 91.43 % of this capacity within 1 min. The saturation hydrogen desorption quantity at 613 K is 6.056 wt%, with 78.24 % of this quantity desorbed within 20 min.