A Co–B alloy/ethylenediamine (EDA) hybrid electrode system has been developed by adding EDA into electrolyte. Charge–discharge measurements show that the inorganic–organic hybrid electrode system exhibits high discharge capacity and long cycle life at elevated temperature (55°C). Specifically, in the electrolyte containing 0.09M EDA additive, the discharge capacity of Co–B alloy electrode after 100 cycles is still up to 601.7mAhg−1 at 55°C. However, for the electrode in EDA-free electrolyte, its discharge capacity is sharply decreased to only 138.5mAhg−1 after 100 cycles. ICP-OES and IR measurements are used to clarify the reason of the improvement in the electrochemical properties. These results show that beneficial effect of EDA on electrochemical properties of Co–B alloy electrode can be attributed to in situ electrochemical oxidation of EDA during discharge cycles. First the oxidation of EDA contributes to part of the discharge capacity and secondly the oxidation products absorbed on the electrode may help to suppress the dissolution of Co at elevated temperature. Evidence is presented suggesting that the oxidation of Co can induce co-oxidation of EDA.