Formation and hydrogen reactivity of MgCo compound

The Mg-Co mixture was milled using a low energy mill during 200 h under argon and then submitted to thermal treatment. The mechanical milling (MM) of Mg-Co mixture leads to microstructural refinement reducing the diffusion distances and then favoring the kinetics of solid-state reaction. As a consequence, the formation of MgCo compound occurs at temperatures of 573 K which is lower than previously reported. As-milled sample (Mg and Co phases) and as-milled plus heated sample (with mainly MgCo compound) were non-isothermally heated under hydrogen pressure using high-pressure differential scanning calorimetric equipment. The presence of MgCo intermetallic compound improves the reactivity with hydrogen, reducing both hydrogen absorption and desorption temperature, as well as increasing the total hydrogen storage capacity. An analysis of the interplay of hydride phases as a function of the starting samples and experimental conditions is presented.