A comparison study of hydrogen storage properties of as-milled Sm5Mg41 alloy catalyzed by CoS2 and MoS2 nano-particles

The influences of the catalysts of CoS2 and MoS2 nano-particles on microstructure and hydrogen storage behaviors of as-milled Sm5Mg41 alloy have been compared in this work. The Sm5Mg41 + 5 wt.% M (M = CoS2, MoS2) alloys were prepared by milling the mechanical ground as-cast Sm5Mg41 alloy powders (particle size ≤ 75 μm) with 5 wt.% CoS2 or MoS2 nano-particles (particle size ≤ 30 nm), respectively. The results demonstrate that the CoS2 and MoS2 nanoparticles are embedded into the alloy surface, which is nanostructure containing some crystal defects, such as dislocation, grain boundary and twin etc. Those microstructures play a beneficial role in reducing the total potential barrier that the hydrogen absorption or desorption reactions must overcome, hence improving the hydrogen storage kinetics of the alloys. The as-milled alloys are composed of Sm5Mg41 and SmMg3 phases, and ball milling refines their crystal grains. The MgH2 and Sm3H7 phases appear after hydrogenation, while Mg and Sm3H7 phases exist after dehydrogenation. The dehydriding activation energy of M = CoS2 and MoS2 alloys are 101.67 and 68.25 kJ/mol H2 respectively. The initial hydrogen desorption of M = CoS2 and MoS2 alloys are 252.9 °C and 247.8 °C. The hydrogenation and dehydrogenation enthalpy changes of M = MoS2 alloy are a little smaller than that of M = CoS2 alloy. Therefore, the catalyst MoS2 can improve the as-milled Sm5Mg41 alloy in hydrogen storage property more effectively than CoS2.