The present communication provides electrochemical impedance spectroscopy (EIS) studies of aluminum addition on Ti{sub}2Ni hydrogen storage alloy electrodes in 6M KOH solution. The experimental results indicate that the electrode without any aluminum addition does not exhibit any passivity but the electrode with aluminum addition (Ti{sub}2Ni{sub}0.97Al{sub}0.03) shows an apparent passivity. Previous XRD results showed the co-existence of a Ti{sub}2Al phase with Ti{sub}2Ni in Ti{sub}2Ni{sub}0.97Al{sub}0.03 alloy. The present EIS studies clearly exhibit the passivity of Ti{sub}2Al electrode. The passivity of the aluminum-containing Ti{sub}2Ni electrode is therefore attributed to the passivity of the co-existing Ti{sub}2Al phase. This further confirms our previous studies of the aluminum addition effect on the performance of the Ti{sub}2Ni electrode and very well explains the cycle life increase and the specific capacity decrease of the aluminum-added electrodes.
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