Photochemical Reactions in the Electrolyte

The Ru(III) complex diffused toward the electrode where it was reduced according to the reaction 

The latter process was responsible for the cathodic current. It must be emphasized that such cathodic currents were only observed with heavily doped Sn02 electrodes. Therefore it was concluded that reaction (73) occurred via tunneling of electrons through the thin space charge layer from the conduction band to Ru(III) molecules produced photochemically.  

Similar relaxation phenomena were also observed with ZnO electrodes and rhodamine B. Gerischer and co-workers interpreted this result by electron transfer from the adsorbed dye (anodic current), followed by a back reaction via tunneling. Any photochemical process or oxygen effect, however, was not mentioned. 

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