Improved Hydrogen Storage Thermodynamics and Kinetics of As-Milled Ce-Mg-Ni-Based Alloys by Adding Ni

Transition metals, especially Ni, are considered highly efficient catalysts for enhancing the characteristics in ad/dehydrogenation of Mg alloy. The Ce₅Mg_95-xNi_x (x = 5, 10, 15) alloys were prepared by mechanical milling technology. The microstructure evolution of all samples during ad/dehydrogenation was characterized by XRD, SEM and TEM. The nanocrystalline and amorphous structure of the as-milled alloys include CeMg₁₂, Mg and Mg₂Ni phases. Increasing Ni content causes a significant increase in the Mg₂Ni phase. By utilizing a Sievert apparatus and analyzing the test results from DSC and TGA, the kinetics of isothermal and non-isothermal hydrogen storage rates were investigated. Both the Arrhenius and Kissinger methods were utilized to estimate the dehydrogenation activation energy. The experimental samples possess exhibit good activation properties and can effectively store 5.0 wt.% of hydrogen. The new specific surface area resulting from the particle pulverization and rupture is responsible for the improved hydrogen sorption kinetics observed during activation. The onset dehydrogenation temperature of the sample decreased from 552.6 to 534.4 K, a reduction of 18.2 K, as the Ni content increased from x = 5 to 15. The dehydrogenation activation energy decreases from 73.68 to 59.99 kJ/mol when Ni is increased, and this is essentially what enhances the hydrogen storage facilitated by nickel substitution. The influence of Ni content variation on the decomposition enthalpy of MgH₂ is minimal. The absolute value of the decomposition enthalpy of MgH₂ (ΔH) decreases from 75.57 to 75.30 kJ/mol as the Ni content increases from x = 5 to 15.