ULTRASOUND IN PHOTOELECTROCHEMISTRY - A NEW APPROACH TO THE ENHANCEMENT OF THE EFFICIENCY OF SEMICONDUCTOR ELECTRODE PROCESSES

A novel photoelectrochemical experiment which simultaneously allows th e illumination of a TiO2 semiconductor electrode surface and the appli cation of power ultrasound emission is described. The horn probe of an immersion horn transducer is modified by an oxide coated titanium tip and placed in a conventional three electrode electrochemical cell whi ch allows light from a monochromated source to be focussed onto the el ectrode surface. Well-defined photocurrents are observed in aqueous me dia and for the photoinduced oxidation of water in acetonitrile and of 2,4-dichlorophenol in acetonitrile. The effect of ultrasound is to sh ift the observed photocurrent responses to more negative potentials an d therefore to enhance the observed processes. Several possible interp retations associated with the complex effects induced by ultrasound ar e considered and a model based mainly on the extreme change of mass tr ansport at the semiconductor/solution interface is suggested. Consider ably enhanced performance for non-Nernstian processes, such as those o bserved in photoelectrochemical reactions at semiconductor electrodes, can be achieved in the presence of ultrasound. (C) 1997 Elsevier Scie nce B.V.