To investigate the effect of Si on the electrochemical properties of crystalline Co, Co-Si samples were synthesized by simple mixing of Co and Si, the electrochemical properties of them were studied as negative electrodes for nickel-metal hydride batteries in aqueous KOH solution. The results show that all the samples possess excellent electrochemical characteristics. When the weight ratio of Co to Si is 4:1, the sample electrode shows the best performance among the as-prepared materials, whose maximum discharge capacity is 419.9mAhg(-1) and the capacity remains 352.2mAhg(-1) after 50 cycles at the discharge current density 25mAg(-1), the retention rate is 83.9%. Analysis of electrode reaction mechanism demonstrates that the discharge capacity is attributed to hydrogenation of Co, where the crucial role Si has a catalytic activity. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.