Abstract:

Amorphous and nanocrystalline PrMg₁₂+x%Ni (x=0, 10, 20, or 30) alloys were prepared by mechanical milling, and the effects of the nickel content on the thermodynamics and kinetics of hydrogen storage in the alloys were studied systematically. The phase composition and microstructure of the alloy were analyzed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The PrMg₁₂+x%Ni (x=0, 10, 20, or 30) alloy was mainly amorphous and nanocrystalline. Before adding nickel, the main phases before and after hydrogen absorption were the PrMg₁₂ phase, MgH₂ phase, and PrH_2.92 phase, respectively. After adding nickel, the main phases before and after hydrogen absorption were a Ni phase, PrMg₁₂ phase, MgH₂ phase, and Mg₂NiH₄ phase. The P-C-T curves and hydrogen absorption and desorption kinetic curves of the alloy were measured using a Sieverts apparatus, and the thermodynamic and kinetic parameters were calculated by combining the Van't Hoff equation, the JMAK model, and the Arrhenius method. The hydrogen desorption enthalpy of the alloy hydride decreased from 89.881 kJ/mol to 82.764 kJ/mol as the Ni content was increased from 0% to 30%, and the hydrogen desorption activation energy decreased from 126 kJ/mol to 90 kJ/mol. Hence, adding nickel can significantly improve the hydrogen release thermodynamics and kinetics of ball-milled PrMg₁₂-type alloy hydrides.

Key words: PrMg₁₂ alloy, mechanical ball milling, hydrogen storage thermodynamics, hydrogen storagedynamics, activation energy