The oxide films of nickel electrode formed in 30 wt.% KOH solution under potentiodynamic conditions were characterized by means of electrochemical, in situ PhotoElectrochemistry Measurement (PEM) and Confocal Microprobe Raman spectroscopic techniques. The results showed that a composite oxide film was produced on nickel electrode, in which aroused cathodic or anodic photocurrent depending upon polarization potentials. The cathodic photocurrent at -0.8 V was raised from the amorphous film containing nickel hydroxide and nickel monoxide, and mainly attributed to the formation of NiO through the separation of the cavity and electron when laser light irradiates nickel electrode. With the potential increasing to more positive values, Ni3O4 and high-valence nickel oxides with the structure of NiO2 were formed successively. The composite film formed in positive potential aroused anodic photocurrent from 0.33 V. The anodic photocurrent was attributed the formation of oxygen through the cavity reaction with hydroxyl on solution interface. In addition, it is demonstrated that the reduction resultants of high-valence nickel oxides were amorphous, and the oxide film could not be reduced completely. A stable oxide film could be gradually formed on the surface of nickel electrode with the cycling and aging in 30 wt.% KOH solution. (c) 2006 Elsevier Ltd. All tights reserved.