Abstract
The bare 
film electrode was found to be unstable during water splitting reactions under illumination of light. Significant improvement of stability was observed for 
covered 
, i.e., 
, thin film electrodes. The 
, layer also enhanced the rate of oxygen evolution instead of 
formation, due to its catalytic effect. The highest photoresponse was found with an 
film prepared at 850°C for 13 min by thermal oxidation. The bandgap energy of both 
and 
films was found to be 2.85 eV. X‐ray diffraction results indicate rutile structure for the 
film. The flatband potential of the 
film was found to be −1.13 V/saturated calomel electrode from the intercept of the Mott‐Schottky plot. The highest potential‐assisted photoconversion efficiencies, 5.1 and 4.1%, and the corresponding practical photoconversion efficiencies, 2.0 and 1.6%, were obtained for water‐splitting by the 
and 
film electrodes, respectively.