Improvement in the hydrogen storage performance of the as-milled Sm–Mg alloys using MoS2 nano-particle catalysts

Abstract

The effects of the addition of MoS₂ catalyst on the microstructure and hydrogen storage behavior of the as-milled Sm₅Mg₄₁ alloys were investigated in this study. The Sm₅Mg₄₁ + x wt% MoS₂ (x = 0, 5, and 10) alloys were prepared by milling MoS₂ powders (particle size ≤ 40 nm) and the mechanically ground as-cast Sm₅Mg₄₁ alloy powders (particle size ≤ 75 μm) in an argon atmosphere for 5 h. The results demonstrate that the as-milled alloys are composed of Sm₅Mg₄₁ and SmMg₃ phases and milling refines the crystal grains. The MgH₂ and Sm₃H₇ phases appear after hydrogenation, while the Mg and Sm₃H₇ phases are formed after dehydrogenation. MoS₂ nano-particles are embedded in the alloy surface, which is nanostructured with some crystal defects, such as dislocations, grain boundaries, and twins. These microstructures are advantageous in reducing the total potential barrier that the hydrogen absorption or desorption reaction must overcome, thus improving the hydrogen storage kinetics of the alloys. The dehydriding activation energies of the alloys are 122.28, 68.25, and 59.91 kJ mol⁻¹ H₂ for x = 0, 5, and 10, respectively. The catalyzed alloys begin to release hydrogen at ∼241.9 °C, which is 26.4 °C lower than the temperature required for non-catalyzed alloys. The hydrogenation enthalpies of the alloys are −81.72, −78.31, and −78.18 kJ mol⁻¹ H₂ for x = 0, 5, and 10, respectively. Therefore, the addition of a MoS₂ catalyst significantly improves the hydrogen storage kinetics of Mg-based alloys.