Plasma Modification of the Surface of Magnesium-nickel Alloy: Enhancement of Oxidation Resistance and Optimization of Hydrogen Storage Kinetics

To address the application bottleneck of magnesium-nickel alloys as hydrogen storage materials, which involves their susceptibility to oxidation and slow hydrogen storage kinetics, this study employed plasma immersion ion implantation technology to modify the surface of Mg₂Ni alloys. The research systematically explored the regulatory laws of process parameters on the surface structure, oxidation resistance, and hydrogen storage kinetics of the alloys. The microstructure of the modified layer was characterized using SEM, XRD, and XPS methods. The performance optimization effect was evaluated through static oxidation experiments, thermogravimetric analysis, and hydrogen absorption/desorption kinetics tests. The results showed that when the plasma treatment power was 400 W, the treatment time was 30 min, and the working pressure was 0.5 Pa, a dense modified layer approximately 2.5 μm thick was formed on the alloy surface, mainly consisting of the composite phase of Ni₃P and MgO. Compared with the unmodified sample, the oxidation rate of the modified alloy in a static oxidation experiment at 600 ℃ for 10 h decreased by 68.3%, and the activation energy of oxidation increased to 186.5 kJ/mol. The hydrogen storage kinetics performance was significantly optimized. At 200 ℃ and 3 MPa hydrogen pressure, the saturated hydrogen absorption time was shortened from 1200 s to 380 s, the hydrogen absorption rate constant increased by 2.1 times, and the storage capacity retention rate after 50 hydrogen absorption/desorption cycles remained at 92.7%, which was 23.5 percentage points higher than that of the unmodified sample. Mechanism analysis indicated that the dense structure of the modified layer could effectively prevent oxygen diffusion to enhance oxidation resistance, while the formation of the Ni₃P catalytic phase and increased surface defects could accelerate the hydrogen adsorption-diffusion process. The proposed plasma modification process provides technical support for the preparation of high-performance magnesium-nickel hydrogen storage alloys and is of great significance for promoting the industrial application of hydrogen storage technology.