Enhanced kinetics of MgH2 via in situ formed catalysts derived from MgCCo1.5Ni1.5

Abstract Magnesium hydride is highly desirable for hydrogen storage due to the high energy density and good reversibility; however, poor thermodynamic and kinetics during dehydrogenation are the main issues for application. Here, to improve the dehydrogenation properties of Mg/MgH2 system, we prepare an Mg/MgH2–MgCCo1.5Ni1.5 composite by ball-milling and hydriding combustion method, in which the in situ decomposition products of MgCCo1.5Ni1.5 compound plays catalytic effect for the de/hydrogenation of the formed MgH2 from Mg. Compared with pure MgH2, the MgH2–MgCCo1.5Ni1.5 composite exhibits a lower initial hydrogen releasing temperature and a faster hydrogen reaction, of which it starts desorbing H2 at 217 °C, 160 °C lower than that of the MgH2. Even at 150 °C, the Mg–MgCCo1.5Ni1.5 composite can reabsorb 5.5 wt% H2 within 60 min. Moreover, the apparent activation energy of the dehydrogenation of composite is reduced to 39.6 kJ/mol from 162.8 kJ/mol. XRD and TEM analyses confirm the formation of Mg2NiH4, MgC0.5Co3 and C during hydrogenation reaction process, where the dehydrogenation of Mg2NiH4 can induce the MgH2 to release hydrogen, the MgC0.5Co3 has a catalytic effect in the composite reaction, and the formed carbon materials help the dispersion of the composite particles.