Synergistic effect of Ni₂Sc and Mg₂Ni on boosting the hydrogen storage kinetic performances of magnesium-nickel alloys

Magnesium-based hydrogen storage materials, with their high hydrogen storage capacity and favorable cost-effectiveness, are promising candidates for addressing the challenges of hydrogen energy storage and transportation. However, their advantages are significantly hindered by high reaction temperatures and sluggish diffusion behavior in the medium-temperature range. To address the issue of sluggish dehydrogenation kinetics, a method for synergistically optimizing the de-/absorption kinetic performance by simultaneously doping with Mg₂Ni and Sc-containing compounds is proposed. By leveraging differences in formation enthalpy, the synthesized material comprises Mg₂Ni, Ni₂Sc, and Mg phases, with the formation of Ni₂Sc inducing microstructural modifications. The formation of Ni₂Sc reduces the Ni concentration in the melt, causing the primary phase in the alloy to shift from Mg₂Ni to Mg. The Mg₈₅Ni₁₄Sc₁ alloy exhibits a hydrogen absorption capacity of 3.6 wt% at 100 ℃ within 105 min, and the hydrogen desorption rate is significantly accelerated. The Mg₂Ni phase is uniformly dispersed within the hydrogen storage particles, while the Ni-Sc compounds are distributed near the particle surfaces. Theoretical calculations indicate that H atoms have lower diffusion energy barriers in Ni₂Sc and Mg₂Ni, with values of 1.60 eV and 1.47 eV, respectively. This arrangement synergistically enhances hydrogen molecule dissociation and atomic hydrogen recombination, resulting in accelerated reaction kinetics. The cooperative effect of these two catalytic phases effectively lowers the endothermic peak temperature of MgH₂ during dehydrogenation by reducing the concentration of H atoms.