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.