Catalytic effect and mechanism of NiCu solid solutions on hydrogen storage properties of MgH2

In this work, the NiCu solid solutions with different Ni/Cu molar ratios were prepared and then doped into MgH2 through ball milling to modify its hydrogen sorption properties. The experimental results show that the Ni–25%Cu and Ni–50%Cu exhibit the superior catalytic effect over pure Ni, pure Cu and Ni–75%Cu on the dehydrogenation of MgH2. Among them, the 5h-milled MgH2/Ni–50%Cu system starts to desorb hydrogen at 205.8 °C, which is about 96.9 °C lower than that of as-milled pristine MgH2. Moreover, the MgH2/Ni-50% Cu system can release 5.14 wt% hydrogen at 300 °C within 15 min, while MgH2 can only release 2.92 wt% hydrogen under the same condition. More importantly, the dehydrogenated MgH2/Ni–50%Cu can reabsorb 4.37 wt% hydrogen even at 250 °C for 30 min. The enhanced hydrogen sorption kinetics of MgH2/Ni–50%Cu mainly attributes to the “hydrogen spillover” effect of in-situ formed Mg2Ni(Cu) phases. Further theoretical calculations reveal that the strong interactions between H and Ni/Cu result in the weakened stability of MgH2, decreased bond strength of Mg–H and enhanced dehydrogenation properties of MgH2. This research provides an important guidance for design multiple transition metals catalysts to improve efficiently hydrogen storage properties of magnesium-based and other metal-based hydrides.