Effect of NiCo2O4 additives on the hydriding properties of magnesium

The effect of NiCo2O4 additives on the hydrogen absorption-desorption characteristics of 85 wt% Mg-15 wt% NiCo2O4 and 95 wt% Mg-5 wt% NiCo2O4 composites prepared by mechanical alloying in an inert atmosphere was investigated. The absorption of hydrogen was measured at temperatures of 573, 473, 423 and 373 K and pressures of 1, 0.4 and 0.2 MPa while the desorption studies proceeded at 573 K under a pressure of 0.15 MPa. The addition of NiCo2O4 was found to exercise a positive effect on the hydriding kinetics of pure magnesium, the absorption capacity remaining high at temperatures below 573 K and pressures lower than 1 MPa. A three-fold decrease of the additive content (from 15 to 5 wt%) did not deteriorate the hydriding kinetics of the composite. After 85 absorption-desorption cycles the composite 95 wt% Mg-5 wt% NiCo2O4 showed no drastic drop in absorption capacity. The favourable absorption-desorption characteristics found for the composites investigated were supposed, on the basis of XPS data, to be due to the catalytic effect of the nickel and cobalt species obtained during hydriding of NiCo2O4 on the sample surface.