Exceptional electrochemical activities of amorphous Fe-B and Co-B alloy powders used as high capacity anode materials

Ultrafine amorphous alloy powders (UAAP) of Fe-B and Co-B were synthesized and tested for possible use as electroactive anodic materials. It is found that unlike their parent elements, the transition metal (TM) and boron, the Fe-B and Co-B alloy powders show superior electrochemical activities when used as anodic materials in aqueous alkaline solution. The discharge capacities of Fe-B and Co-B electrodes were observed to be 1200 and 1100 mAh/g at moderately high rate of 100 mAh/g, respectively, much higher than the theoretical capacity of currently used zinc metal (820 mAh/g). The exceptional high capacities of the boride alloys were found due to the electrochemical activation of boron atoms in the highly dispersed transition metal atoms. Inversely, the activated boron clamps the electrode potential to a negative region to prevent the transition metal from passivating. (C) 2004 Elsevier B.V. All rights reserved.