Electrochemical Properties of Polycrystalline TiO2 Electrodes Prepared by Anodic Oxidation

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Abstract
Polycrystalline electrodes were characterized by electroluminescence and capacitance‐voltage measurements. The intensity of electroluminescence in a polycrystalline was about two orders of magnitude larger than that in a single crystalline . Due to the intensive light emission which could be seen with the naked eye, a spectroscopic analysis by using a monochromator was possible. The emission spectrum showed a broad band peaked at 570 nm, which was assigned to a radiation recombination of a hole injected from the electrolyte with an electron on the surface state, the distribution of which was estimated from the C‐V measurements. Mott‐Schottky plots for a polycrystalline showed little frequency dispersion. Cole‐Cole plots could be fitted by two semicircles. Through the analysis of relaxation times, charging and discharging process at the electrode surface could be clarified. The analysis of the impedance data have revealed that the surface state is distributed from the conduction bandedge to the midgap in the forbidden gap. The surface‐state density falls with energy from the conduction band. It has been concluded that the dynamic electron distribution of the surface states, which is determined by the competitive charge transfer process of electrons and holes injected from the electrolyte and from the semiconductor determines the luminescence characteristics of this material.

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