Stability and photoresponse of nanocrystalline n-TiO{sub 2} and n-TiO{sub 2}/Mn{sub 2}O{sub 3} thin film electrodes during water splitting reactions

The bare n-TiO{sub 2} film electrode was found to be unstable during water splitting reactions under illumination of light. Significant improvement of stability was observed for Mn{sub 2}O{sub 3} covered n-TiO{sub 2}, i.e., n-TiO{sub 2}/Mn{sub 2}O{sub 3}, thin film electrodes. The Mn{sub 2}O{sub 3}, layer also enhanced the rate of oxygen evolution instead of H{sub 2}O{sub 2} formation, due to its catalytic effect. The highest photoresponse was found with an n-TiO{sub 2} film prepared at 850 C for 13 min by thermal oxidation. The bandgap energy of both n-TiO{sub 2} and n-TiO{sub 2}/Mn{sub 2}O{sub 3} films was found to be 2.85 eV. X-ray diffraction results indicate rutile structure for the n-TiO{sub 2} film. The flatband potential of the n-TiO{sub 2} film was found to be {minus}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 n-TiO{sub 2} and n-TiO{sub 2}/Mn{sub 2}O{sub 3} film electrodes, respectively.