Semiconductor corrosion energy diagrams

Figure 29.4 shows an example, the energy diagram of a cell where n-type cadmium sulfide CdS is used as a photoanode, a metal that is corrosion resistant and catalytically active is used as the (dark) cathode, and an alkaline solution with S and S2 ions between which the redox equilibrium S + 2e 2S exists is used as the electrolyte. In this system, equilibrium is practically established, not only at the metal-solution interface but also at the semiconductor-solution interface. Hence, in the dark, the electrochemical potentials of the electrons in all three phases are identical. 

Fig. 5.13 Energy level diagram comparing the surface band edge positions of SnS and the energies corresponding to selected redox couples and corrosion reactions involving the semiconductor. (Reproduced from [198])...

Fig. 13. Diagram illustrating corrosion of a semiconductor (a) through both energy bands, and (b) through the valence band.

In order to find out whether a semiconductor is liable to electrolytic or corrosion decomposition in any particular system, let us consider the energy-band diagram which plots the electrochemical potential levels for the decomposition reactions (39a) and (39b). 

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