Shape-dependent photogenerated cathodic protection by hierarchically nanostructured TiO2 films

TiO2 films with different nanostructures were prepared by means of hydrothermal technique by adjusting the concentration of reactant components and reaction time. The flower-like, rod-like and sphere-like of the TiO2 films were observed by scanning electron microscopy. The shape-dependent photogenerated cathodic protection activity of such films were investigated. The flower-like film presents the largest drop of open circuit potential and the maximum magnitude of the photocurrent once irradiated by UV light. The 304 stainless steel coupled with it has the most negative potential Ecorr in comparison with other nanostructure films as well. The electrochemical impedance spectroscopy analysis of 304 stainless steel also shows the minimum charge transfer resistance when coupled with flower-like nanostructure films. To understand the effect of nanostructure on the properties, possible schematic diagrams of UV incident light passage in the three flower-like, rod-like and sphere-like nanostructures films are proposed to explain the absorption difference. The flower-like structure with a large amount of voids is beneficial to enhance light scattering and trapping for efficient UV light harvesting.