The oxidation behaviors of Ni and Ni-Co alloy electrodes were investigated using simple electrochemical techniques under an O-2 + CO2 gas mixture in the ratio of 9:1 at a total pressure of 1 atm at 650 degrees C. In situ oxidation processes of Ni, Ni-10Co and Ni-25Co as opposed to Ni-50Co demonstrate 3 and 4 potential plateaux, respectively. The final plateau for all electrodes approached the oxygen potential. Nucleation and growth of the oxide were represented by the first and second plateaux, respectively. For Ni-50Co electrode, however, an additional plateau due to the formation of LiCoO2 was observed. The lithiation took place by chemical reaction at the oxide growth step. Between the lithiated NiO and (Ni, Co)O produced by in situ oxidation of porous Ni and Ni-Co alloy plaques, the solubility of(Ni, Co)O was found to be lower than that of NiO. As the Co concentration in the oxide is increased, the solubility is decreased. Extension of cathode life time appears possible if the Ni cathode is modified by the addition of Co.