We have investigated the effect of prolonged cycling on the hydriding/dehydriding properties and on the structure of nanocrystalline MgH2–V composite produced by high-energy ball milling. The hydrogen charge and discharge kinetics of the nanocomposite hydride were tested at 300°C using up to 2000 cycles. Pressure composition isotherms at 300°C were also carried out. The nanocomposite exhibits good reversibility in its hydrogenation/dehydrogenation curves after 2000 cycles. The results show some improvements in hydrogen capacity during cycling; this enhanced H-solubility is believed to be the result of structural relaxation. The sample resistance to hydrogen decrepitation was also evaluated via additional experiments involving SEM, BET specific surface area and X-ray crystal structure characterisations. These observations indicate that the nanostructured Mg-based composite does not decrepitate much upon cycling. However, a slight deterioration in the discharge rate of the nanocrystalline magnesium hydride is observed, apparently related to the crystal growth during cycling.

Influence of cycling on the thermodynamic and structure properties of nanocrystalline magnesium based hydride