The electrochemical hydrogen storage properties of the ball-milled PrMg12 Ni-x(x) + 150 wt% Ni (x = 1 and 2) composites were investigated, and compared with those of the ball-milled PrMg12 + 150 wt% Ni composite. The ball-milled PrMg11Ni-Ni composite has the highest initial discharge capacity (973 mAh/g) and high-rate dischargeability (HRD). The cycle life improves with the increase of Ni content, which was confirmed by the XRD results of the ball-milled composites after 10 cycles. By means of electrochemical impedance spectra, linear polarization and anodic polarization measurements, the electrochemical kinetic parameters were studied. it is suggested that the high hydrogen diffusivity and moderate reaction resistance are responsible for the higher discharge capacity and HRD of the PrMg11Ni-Ni sample, while the lower discharge capacity and HRD of the PrMg10Ni2-Ni sample is probably due to the excessively high reaction resistance. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved