Abstract
The competition between the anodic dissolution of an illuminated n-GaAs electrode and the anodic oxidation of tetramethyl- p-phenylenediamine (TMPD) was studied quantitatively by rotating ring-disk voltammetry as a function of the photocurrent density, the TMPD concentration, the pH of the solution and the water-to-methanol ratio of the solvent. From the results, it is concluded that the first electrochemical step of the dissolution process is followed by a chemical step in which the surface intermediate formed reacts with a water molecule, and that the subsequent electrochemical steps may involve either a free hole or a surface intermediate as the mobile surface species, depending on the composition of the electrolyte apart from the redox system.
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