Catalytic effect of MoS2 on hydrogen storage thermodynamics and kinetics of an as-milled YMg11Ni alloy

Abstract

In this study, YMg₁₁Ni and YMg₁₁Ni + 5 wt% MoS₂ (named YMg₁₁Ni–5MoS₂) alloys were prepared by mechanical milling to examine the effect of adding MoS₂ on the hydrogen storage performance of a Y–Mg–Ni-based alloy. The as-cast and milled alloys were tested to identify their structures by X-ray diffraction and transmission electron microscopy. The isothermal hydrogen storage thermodynamics and dynamics were identified through an automatic Sieverts apparatus, and the non-isothermal dehydrogenation performance was investigated by thermogravimetry and differential scanning calorimetry. The dehydrogenation activation energy was calculated by both Arrhenius and Kissinger methods. Results revealed that adding MoS₂ produces a very slight effect on hydrogen storage thermodynamics but causes an obvious reduction in the hydrogen sorption and desorption capacities because of the deadweight of MoS₂. The addition of MoS₂ significantly enhances the dehydrogenation performance of the alloy, such as lowering dehydrogenation temperature and enhancing dehydrogenation rate. Specifically, the initial desorption temperature of the alloy hydride lowers from 549.8 K to 525.8 K. The time required to desorb hydrogen at 3 wt% H₂ is 1106, 456, 363, and 180 s corresponding to hydrogen desorption temperatures at 593, 613, 633, and 653 K for the YMg₁₁Ni alloy, and 507, 208, 125, and 86 s at identical conditions for the YMg₁₁Ni–5MoS₂ alloy. The dehydrogenation activation energy (E_a) values with and without added MoS₂ are 85.32 and 98.01 kJ mol⁻¹. Thus, a decrease in E_a value by 12.69 kJ mol⁻¹ occurs and is responsible for the amelioration of the hydrogen desorption dynamics by adding a MoS₂ catalyst.