The electrochemical impedance of one-equivalent electrode processes at dark semiconductor|redox electrodes involving charge transfer through surface states.: 1.: Theory

Electrode processes at redox electrodes consist of mass transport to and from the electrode\electrolyte interface and of charge transfer across this interface. At n-type semiconductor electrodes, charge transfer may involve either direct exchange of conduction band electrons or direct exchange of valence band holes, accompanied by an electron-hole recombination step, or surface-state mediated transfer of conduction band electrons. In this paper, the electrochemical impedance of the dark n-type semiconductor\redox electrode is derived, taking into account both mass transport and charge transfer through surface states. The impedance expression obtained leads to a novel equivalent circuit. More limited calculations, previously published in the literature, are comprised in the treatment as special cases. Finally, it is shown how the impedance expression obtained may be also used to describe reactions involving direct exchange of majority charge carriers or direct injection of minority charge carriers followed by a recombination step.