Preparation, Microstructure and Photoelectrochemical Properties of Co Doped Titanium Oxide Electrodes

The Co doped titanium oxide film was prepared on pure titanium plates by sol-gel dip-coating technique using Co(Ⅱ) metal salts and tetrabutyltitanate (Ti(OC4H9)4) as precursors. The microstructure and photoelectrochemical properties of 5%Co doped-TiO2 film photoelectrode were investigated by scanning electron microscopy (SEM), X-ray diffraction, photocurrent response spectra, etc.The wavelength of the light source in the experiment was more than 460 nm. Various Co(Ⅱ) metal salts (Co(NO3)2, Co(AC)2 and CoSO4) were chosen to compare the influence of different dopant precursors and the photocurrent response spectra showed that Co (AC)2 was better than the other two. Thus, the work focused on Co(AC)2 dopant. It was found the photoelectric efficiency of %Co doped-TiO2 film photoelectrode was remarkably higher than that of pure TiO2 film photoelectrode. It suggested that suitable content of doped Co(Ⅱ) in TiO2 can efficiently extend the light absorption properties to the visible region, which was probably due to the fact Co(Ⅱ) can generate crystal effect on TiO2 crystal lattice. The amount of doped Co(Ⅱ) was an important factor affecting photocatalytic activities, the optimum amount of doped Co(Ⅱ) was 5%. With increasing the content of doped Co, the separate phase of CoTiO3 appeared, which reduced the value of photocurrent of 5%Co doped-TiO2/Ti film electrode. Furthermore, excessive doped Co(Ⅱ) promoted the anatase-rutile phase transformation process and reduced the temperature of phase transition. In addition, when the heating temperature was above 500℃, the X-ray diffraction showed few sperate phases of CoTiO3appeared and some anatase phases converted to rutile phases. 5%Co-doped-TiO2/Ti electrode formed at 500℃with 2 coating layers had the highest photoelectric efficiency under the visible light (λ>460 nm).