Air-stable MgH2 − CeO2 composite with facilitated de/hydrogenation kinetics synthesized by high energy ball milling

The oxidation of Mg seriously limits its long-life applications as a hydrogen storage material. Considering the catalytic effects and unique redox instincts of rare earth oxides, MgH2 with CeO2 on the surface has been prepared by high energy ball milling MgH2 with CeO2 (20 wt%) in Ar and air atmosphere, respectively. It is expected to improve the oxidation resistance of Mg and elucidate the underlying mechanism by detailed microstructure observation and de-/hydrogenation kinetics analysis. CeO2 with particle size in the range of ~ 20-100 nm are uniformly distributed on the surface of MgH2 matrix after milling. For pure MgH2 milled in air, both hydrogen capacity and de-/absorption kinetics deteriorate evidently comparing with those of pure MgH2 milled in Ar. However, both MgH2 + CeO2 milled in Ar and air can rapidly absorb and desorb hydrogen. MgH2 + CeO2 milled in air can absorb ~ 4 wt% hydrogen within 4 min at 300 °C. For pure MgH2 milled in Ar after air exposure, a long incubation period is necessary before fast dehydrogenation, while fast desorption is still observed for air-exposed MgH2 + CeO2. It is believed that the uniformly distributed cerium oxides, which serve as catalysts promoting recombination of hydrogen and nucleation of new phase, can effectively prevent forming a dense and continuous MgO layer on the MgH2 surface during air exposure due to the unique instincts of CeO2. The obtains in this work can be expected to provide guidelines to ameliorate the oxygen-free conditions of Mg-based hydrogen storage alloys by selecting proper catalyst and reasonable processing.