Surface modification of hydrogen storage alloy electrode with an alkaline solution containing potassium borohydride as a reducing agent

Negative electrodes consisting of MmNi3.6Mn0.4Al0.3Co0.7 alloy in porous nickel substrate were modified by immersing them in an alkaline solution of potassium borohydride (KBH4). Such a simple modification results in rapid activation and increases the saturation capacity and high-rate dischargeability of the negative electrodes. Electrochemical analysis indicates that the overvoltages in charging and discharging processes were drastically decreased by the reducing treatment. Electrons liberated from borohydride ions and intermediary hydrogen play an important role for improving the characteristics of negative electrodes. The evidence for hydride formation during the surface modification was detected by X-ray diffraction measurements as well as by an electrochemical method.