The Synergistic Effect of Ni–Mo–S in Promoting the Hydrogen Storage Performance of Magnesium Hydride

Catalytic doping is considered one of the most efficient strategies to achieve superior performance of MgH2, as rationally designed catalytic components can exhibit synergistic effects, thereby optimizing the kinetic pathways. In this study, the hydrothermal method was adopted to prepare clustered Ni–Mo–S catalysts, which were used to modify MgH2 to enhance its kinetic performance. Experimental results demonstrate that the molar proportion of Ni to Mo significantly impacts the modification effect of Ni–Mo–S catalysts on MgH2. Furthermore, the catalyst whose molar ratio of Ni/Mo is 7:2 achieves the optimal catalytic efficiency. Specifically, at 125 °C, MgH2-5 wt % Ni–Mo–S can absorb 4.61 wt % H2 in 1200 s. At a relatively low temperature of 250 °C, it manifests a rapid dehydrogenation rate and releases 5.81 wt % H2 in 2000 s. The hydrogenation (41.98 kJ/mol) and dehydrogenation (86.41 kJ/mol) activation energies of MgH2-5 wt % Ni–Mo–S are reduced by 48.87 and 43.79% compared to as-milled MgH2, respectively. Mechanism analysis suggests that this improvement may be ascribed to the following reasons: (1) The hydrogen pump effect of Mg2Ni/Mg2NiH4 facilitates the hydrogen diffusion; (2) electron transfer between Mo species with different valence states weakens the Mg–H bonds; (3) the in situ formed MgS serves as diffusion channels for hydrogen atoms, expediting hydrogen transport. This work provides a valuable outlook for constructing highly active catalysts for MgH2 hydrogen storage.