AN INVESTIGATION OF CHARGE-TRANSFER PROCESSES AT N-TIO2 BY USING A SHORT LASER-PULSE

The charge-transfer processes at illuminated n-TiO2 electrodes have be en investigated using a nitrogen laser. The initial photopotential to the second power linearly depends on electrode potential for poly- and single-crystalline electrodes. It allows us to use photopotential mea surements to determine the flatband potential. For polycrystalline ele ctrodes far from the flatband potential, the characteristic time of ph otopotential decay (tau) is determined by electric discharge through a n external circuit (tau = RC). The dependence of 1/tau2 vs. E is a str aight line, but the intersection with a potential axis is shifted in t he cathodic direction by 0.4 V from the flatband potential. This is ex plained by the assumption that there is some capacitance connected in series with space-charge capacitance. From the analysis of the photopo tential decay curves for a polycrystalline electrode, the rate of char ge transfer from a semiconductor to an electrolyte solution was estima ted to be less than 10(2) s-1. Near the flatband potential, the recomb ination photocurrent with relatively slow time decay was observed. The model which provides the explanation of these phenomena is proposed a nd discussed.