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.