Ea. Ponomarev et al., AN INVESTIGATION OF CHARGE-TRANSFER PROCESSES AT N-TIO2 BY USING A SHORT LASER-PULSE, Journal of the Electrochemical Society, 140(10), 1993, pp. 2851-2857
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.