Cyclic voltammetry CV at semiconductor electrodes

The various redox couples used in this experiment and their potentials on Ti02 and Pt are listed in Table 9.1. The idea was to judge the position of energy bands based on the reversibility of the CV for redox couples of known potentials. Based on these results, three 

Reprinted with permission from reference (33). Copyright 1975, American Chemical Society. 

with the help of voltaimnetric experiments in a judiciously chosen redox couple, one can pinpoint various energy states in the bulk as weU as on the surface of the semiconductor, This model was further supported by CV results obtained on WSc2 in aqueous solution (34, 35), GaAs in molten salt (36), Si, n-type ZnO, CdS, and GaP electrodes in acetonitrile (21), and CdS, GaP, GaAs, and p-type Ge in V,V -dimethylformamide (37). 

This situation indicates that the electrode is degenerated at that potential and behaves like a metal. The second oxidation wave appears on illumination, which was not seen in dark. As discussed in Section 9.4.2, photo-oxidation at an n-type semiconductor is prevalent if the redox potential lies within the band gap. Thus, the second wave observed upon illumination was assigned to the oxidation of TMPD+ to TMPD + or BF to BF. Quite interestingly for BF, the CVs recorded in the dark and under illumination are separated by approximately 0.20 V. The onset of a photocurrent for both TMPD and BF is at 

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