The Electrochemical Impedance of One-Equivalent Electrode Processes at Dark Semiconductor/Redox Electrodes Involving Charge Transfer through Surface States. 2. The n-GaAs/Fe3+ System as an Experimental Example

In this paper, an electrochemical study of the n-GaAs/Fe 3+ system is presented. Combining the results of current density vs potential, Mott−Schottky, and electrochemical impedance measurements, it is shown that charge transfer through surface states is the most plausible reaction mechanism for the Fe 3+ to Fe 2+ reduction at the n-GaAs electrode. On the basis of the experimental impedance spectra and of the theoretical equivalent circuit derived in part 1 (Hens, Z. J. Phys. Chem. 1998, 103, 122), the charge-transfer mechanism is analyzed in detail. The Fe 3+ reduction rate shows a marked evolution as a function of time which, basing upon the electrochemical impedance results, is attributed to an increase in the number of surface states.