Abstract:

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.

Key words: Sm₅Mg₄₁ alloy, CoS₂ and MoS₂ catalyst, Milling, Activation energy, Hydrogen storage kinetics