Electrode Reactions in Electrolytes without Redox Systems

Electrode Reactions in Electrolytes without Redox Systems 

During polarization, various electrode processes can occur such as electrochemical dissolution, O2 evolution and oxide formation during anodic polarization, and surface reduction and H2 formation during cathodic polarization. It must be emphasized that the theory derived above is not quantitatively applicable here because, in most processes, a strong interaction between semiconductor and electrolyte is involved, whereas the electron transfer theory is only valid for weak interactions, i.e., it is applicable only for redox processes. The other processes, electrochemical dissolution, etc., will be treated briefly before discussing pure electron transfer reactions (redox processes) because they present the basic behavior of semiconducting electrodes. 

Similar conclusions can be made for anodic processes. Since here a current increase is only observed with p-type electrodes, it can be concluded that the dissolution process is a valence band process. The density of holes at the surface determines the reaction rate. 

These basic properties of semiconductor electrodes were observed at first by Brattain and Garrett with germanium electrodes. It was further shown for germanium that the small cathodic current at p-type and small anodic current at n-type germanium are quantitatively determined by the diffusion of minority carriers.  

Decomposition Products of Various Semiconductor Electrodes during Anodic and Cathodic Poiarization  

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