Effects of electronic excitation on reaction rates at the solid-eletrolyte interface

One of the central problems of electrochemistry is the understanding of charge transfer reactions at the solid-electrolyte interface. In such reactions, electronic interactions are altered and chemical bonds are changed or modified. It is obvious that electronic excitation of the involved species which is usually obtained by light absorption will effect the reaction rate or even the reaction products. The excitation of electronic states, present at the interface between a solid and an electrolyte can effect electron transfer processes as well as ion transfer steps. The efficiency depends on the lifetime of the excited states and on the rate of the reactions. Due to the high rate of electron transfer, such a process is much more frequently accelerated by electronic excitation than ion transfer. Examples are discussed for both cases with excitation at the interface either on the side of the solid (metals, semiconductors, or insulators) or of the electrolyte. In the solid, effects caused by excited electrons or excited holes can be distinguished. Excitation in the electrolyte serves as a model for a mechanism of spectral sensitization. The generation of photo-voltages at a semiconductor electrolyte interface could possibly be used for energy conversion. (author)