Synthesis, characterization and hydrogen storage properties of Mm(Ni, Co, Mn, Al)5 alloy

This paper investigates hydrogenation characterizations and the effect of hydrogenation/dehydrogenation (H/D) cycling on the structural and morphological properties of MmNi 4.22Co0.48Mn0.15Al0.15 (Mm=mischmetal) alloy. The alloy was prepared using an arc melting method followed by multiple re-melting under an argon atmosphere. Results indicate that the alloy is pulverized into fine particles after several H/D cycles while retaining its hexagonal LaNi 5-type structure. Pressure-composition isotherms for H/D reactions and absorption kinetics were measured across a temperature range of 293-338K. The absorption plateau pressures reached ~0.51, 1.22, and 2.49 bar at 293, 313, and 333K respectively, with a maximum hydrogen storage capacity observed at approximately 5.78 wt% at 293K. The enthalpy (∆H), entropy (∆S), and activation energy for the reactions (E a) were calculated, demonstrating that the hydrogenation reaction rate increases with higher operating temperatures or pressures. Jander diffusion (JDM) and Johnson-Mehl-Avrami (JMA) models were utilized to analyze the kinetic mechanisms of the hydrogenation process in detail. The findings suggest that the MmNi 4.22Co0.48Mn0.15Al0.15 alloy holds potential for practical applications.