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

In this study, YMg 11 Ni and YMg 11 Ni + 5 wt% MoS 2 (named YMg 11 Ni-5MoS 2 ) alloys were prepared by mechanical milling to examine the effect of adding MoS 2 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 MoS 2 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 MoS 2 . The addition of MoS 2 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% H 2 is 1106, 456, 363, and 180 s corresponding to hydrogen desorption temperatures at 593, 613, 633, and 653 K for the YMg 11 Ni alloy, and 507, 208, 125, and 86 s at identical conditions for the YMg 11 Ni-5MoS 2 alloy. The dehydrogenation activation energy ( E a ) values with and without added MoS 2 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 MoS 2 catalyst. MoS 2 nanoparticles embedded into alloys markedly enhance the dehydrogenation performance, such as lowering dehydrogenation temperature and enhancing dehydrogenation rate.