Electrochemical hydrogen storage of ball-milled MmMg12 alloy–Ni composites

MmMg12–Ni amorphous or nanocrystalline composites (Mm: Ce-rich mischmetal) were prepared through the ball-milling method, and their electrochemical hydrogen storage performance was investigated and compared with that of ball-milled CeMg12–Ni composites. It was found that the ball-milled MmMg12–Ni composites had larger initial discharge capacities and better high rate dischargeability. Analysis of electrochemical impedance spectra (EIS) shows that the reaction resistance and hydrogen diffusion resistance of the ball-milled MmMg12–Ni composites are lower as a result of the decrease in Ce content, and thus can contribute to the larger discharge capacity and better high rate dischargeability. Additionally, the cycle performance of the ball-milled MmMg12–Ni composites is better than those of the ball-milled CeMg12–Ni composites. This may be related to the formation of a Nd oxide or Nd(OH)3 film on surface of the MmMg12 alloys.