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

In this study, a MgH 2 –Ru composite is prepared by mechanical ball milling of MgH 2 and Ru powders. The microstructural analysis revealed the uniform distribution of Ru nanoparticles in the MgH 2 matrix and the formation of intermetallic compounds (i.e. Mg 6.2 Ru and Mg 1.5 Ru) after dehydrogenation of the composite. The substantial improvements in the de/hydrogenation properties of MgH 2 are due to the adjustable catalytic role of Ru under low temperature and pressure conditions. MgH 2 –Ru composite started to release hydrogen at an onset temperature of 300 °C, much lower than the mechanically milled pure MgH 2 (350 °C). Hydrogen absorption of the MgH 2 –Ru composite is relatively fast at 350 °C and stored 6.1 wt% in 5 min. At the same temperature, the hydrogenated MgH 2 –Ru composite released all stored hydrogen in less than 5 min. Compared with the catalyst-free MgH 2 , the hydrogenation and dehydrogenation activation energies of the MgH 2 –Ru composite are reduced to 65.12 ± 2.4 kJ/mol H 2 , and 97.46 ± 4.15 kJ/mol H 2 , respectively. In addition, it further demonstrated how the reversible transformation of Mg–Ru intermetallic phases induces the thermodynamic destabilization of the MgH 2 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 MgH 2 .