Enhancing (de)hydrogenation kinetics properties of the Mg/MgH_2 system by adding ANi_5(A=Ce,Nd,Pr,Sm,and Y) alloys via ball milling

Magnesium (Mg)-based alloys have already been widely studied as the hydrogen storage materials because of their high reversible hydrogen storage capacity, low cost, light weight, etc. However, the poor de/hydrogenation kinetic properties dramatically hinder the practical applications. In this work, the MgH₂-ANi₅ (A = Ce, Nd, Pr, Sm, and Y) composites were prepared by a high-energy ball milling method, which can effectively refine the particle size thus improving the kinetic properties. Experimental results reveal that the MgH₂-ANi₅ composites mainly consist of Mg₂NiH₄, MgH₂ and rare earth (RE) hydride, which will be dehydrogenated to form Mg₂Ni, Mg and stable RE hydride reversibly. Accordingly, the as-milled MgH₂-ANi₅ (A = Ce, Nd, Pr, Sm, and Y) composites with various A-elements can respectively contribute to a reversible hydrogen storage capacity of 6.16 wt%, 5.7 wt%, 6.21 wt%, 6.38 wt%, and 6.5 wt% at a temperature of 300 °C, and show much better kinetic properties in comparison to the pure MgH₂ without any additive. In-situ formed Mg₂Ni and stable RE hydride (such as CeH_2.73 and YH₂) might act as effective catalysts to significantly improve the hydrogen storage properties of MgH₂. The present work provides a guideline on improving the kinetic properties of the Mg-based hydrogen storage alloys.