Photoreduction Processes on n‐TiO₂ Electrodes

Abstract

Abstract Photoelectrochemical processes are repeatedly suggested to be utilized for the conversion of light into electrical and/or chemical energy. This study reports on photoreduction processes which can be obtained on cathodically polarized n‐TiO 2 electrodes when reducible species such as O 2 , Fe 3+ , Ce 4+ , Fe(CN) 3‐ 6 , and H 2 O 2 are present in the electrolyte. The changes of photoreduction are investigated as function of the amount of reducible species transported to the surface as well as the wavelength and intensity of the incident light. It is shown that under specific experimental conditions the cathodic quantum efficiency η c can reach values up to 1. An energy scheme is suggested to explain the mechanism which is responsible for the photoreduction process. In this scheme a broad distribution of surface states is introduced which covers the forbidden gap of the semiconductor from a mid‐gap position up to levels close to the tower edge of the conduction band E CB . It is assumed that these surface states mediate the transfer of electrons and holes from the illuminated electrode to the solution. Possible reaction channels are discussed.