The adaptable effect of Ru on hydrogen sorption characteristics of the MgH2 system

Abstract

In this study, a MgH2–Ru composite is prepared by mechanical ball milling of MgH2 and Ru powders. The microstructural analysis revealed the uniform distribution of Ru nanoparticles in the MgH2 matrix and the formation of intermetallic compounds (i.e. Mg6.2Ru and Mg1.5Ru) after dehydrogenation of the composite. The substantial improvements in the de/hydrogenation properties of MgH2 are due to the adjustable catalytic role of Ru under low temperature and pressure conditions. MgH2–Ru composite started to release hydrogen at an onset temperature of 300 °C, much lower than the mechanically milled pure MgH2 (350 °C). Hydrogen absorption of the MgH2–Ru composite is relatively fast at 350 °C and stored 6.1 wt% in 5 min. At the same temperature, the hydrogenated MgH2–Ru composite released all stored hydrogen in less than 5 min. Compared with the catalyst-free MgH2, the hydrogenation and dehydrogenation activation energies of the MgH2–Ru composite are reduced to 65.12 ± 2.4 kJ/mol H2, and 97.46 ± 4.15 kJ/mol H2, respectively. In addition, it further demonstrated how the reversible transformation of Mg–Ru intermetallic phases induces the thermodynamic destabilization of the MgH2 system. The presence of Ru not only facilitated the breaking of the Mg–H bond but also provided very good catalytic interfaces for enhanced de/hydrogenation properties of MgH2.