The first study on enhanced photoresponsivity of ZnO-TiO₂ nanocomposite thin films by anodic polarization

The physical and photoelectrochemical properties of the anodized ZnO-TiO₂ thin films were investigated in this study. Impedance spectroscopy revealed a decrease in charge transfer resistance and Tafel plots determined enhancement of about 200 times in the exchange current (i ₀) after anodization at high positive potential. It was found from XPS analysis that after applying the potential of 5 V to the ZnO-TiO₂ photoelectrode, the lattice oxygen (O^2-) in the thin film is oxidized to molecular oxygen and then, cations such as Zn²⁺ can be solved in the basic electrolyte and passed to the solution. Moreover, according to AFM analysis it was observed that the surface of the samples has been grooved by applying anodic voltage resulting in an increase of effective surface of the film. A mechanism for describing the significant enhancement in the photoresponse of the anodized layer is proposed.