Improving the hydrogenation properties of MgH2 at room temperature by doping with nano-size ZrO2 catalyst

Recent studies have shown that the hydrogen absorption-desorption kinetics in magnesium can be improved by milling magnesium hydride (MgH2) with transition metal oxides. Accordingly, the present study investigates the particle size, crystalline structure and hydrogen absorption properties of MgH2 composite samples containing zirconium dioxide (ZrO2) nano-powder in molar fractions ranging from 1 to 5%. Hydrogen absorption kinetics isotherms are presented for temperatures in the range of 25-150 °C. The hydriding processes and kinetics of MgH2-ZrO2 alloy powers at different temperatures have also been studied. By theoretical analysis of the experimental data of the pyrolytic hydriding reaction, and fitting this with the Johnson-Mehl-Avrami (JMA) equation, the kinetic equation and the corresponding kinetic parameters, including the reaction order, the reaction rate constant, and the reaction activation energy, have been obtained. In general, the results show that ZrO2 acts as a refining agent, and is thus beneficial in decreasing the MgH2 activation energy and reducing the crystalline size during the milling process.