Boosting hydrogen storage performance of hyper-eutectic Mg-Ni alloys via Cu doping: Synergistic regulation of Mg₂Cu-Mg₂Ni dual phases

Hypereutectic Mg-Ni alloys exhibit excellent thermodynamic properties but suffer from limited kinetic performance. In this study, Mg₄₀Ni_10-xCu_x (x = 0, 2, 4) alloys with the same morphology as Mg₂Ni/Mg₂Cu-Mg were prepared to utilize the synergistic effect of Cu and Ni for improving the hydrogen storage kinetic performance. Partial substitution of Ni with Cu in the Mg₂Ni-rich matrix modifies the morphology of both primary Mg₂Ni and eutectic Mg-Mg₂Ni phases, with Cu existing in the form of Mg₂Cu. As the Cu content increases, the hydrogen storage capacity and the kinetics of hydrogen absorption and desorption are significantly enhanced. The Mg₄₀Ni₈Cu₂ alloy achieves a maximum hydrogen absorption capacity of 5.57 wt% at 225°C. At 250°C, it absorbs 4.09 wt% hydrogen within 20 min and desorbs 3.6 wt% within 3 min, representing the fastest absorption/desorption rates among the studied compositions. The incorporation of Cu reduces the apparent activation energy for dehydrogenation, lowering the hydrogen release activation energy from 74.55 to 50.46 kJ/mol. Kinetic analysis indicates that rising temperature shifts the hydrogenation mechanism from interface to diffusion control. This transition, combined with the Mg-Cu/Mg-Ni dual-phase synergistic regulation that markedly facilitates the nucleation and diffusion, collectively enables superior hydrogen storage kinetics.