MmMg(12)-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 CeMg(12)-Ni composites. It was found that the ball-milled MmMg(12)-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 MmMg(12)-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 MmMg(12)-Ni composites is better than those of the ball-milled CeMg(12)-Ni composites. This may be related to the formation of a Nd oxide or Nd(OH)(3) film on surface of the MmMg(12) alloys. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.