Charge efficiency of misch metal-based hydrogen storage alloy electrodes at relatively low temperatures

Charge efficiency of Mm (misch metal)-based hydrogen storage alloy (MmNi(3. 6)Mn(0.4)Al(0.3)Co(0.7)) electrode was evaluated in the temperature range o f 25 to -40 degreesC. The charge efficiency obviously decreased less than 0 degreesC. From the rate of hydrogen absorption in solid-gas phase, exchang e current density and charge-transfer resistance measured at various temper atures, it was inferred that the rate-determining step in the charge proces s of the negative electrode at relatively low temperatures was the charge-t ransfer reaction on the electrode surface. The addition of Mo to the alloy was effective for improving the electrocatalytic activity, leading to the i mprovement of the charge efficiency at relatively low temperatures. (C) 200 1 Elsevier Science Ltd. All rights reserved.