Determination of rate constants for dark current reduction at semiconductor electrodes using ZnO single-crystal microelectrodes

A method based on microelectrodes of ZnO single crystals was employed to de termine the effective reaction velocity for dark reduction of ferrocenium a ccepters by electrons from the semiconductor conduction band. Measurement t echniques were explored and theoretical models for steady-state voltammetry at semiconductor electrodes developed. The microelectrode method as presen ted here represents an unambiguous experimental method for ascertaining ide al interfacial behavior even at high current flows found near the flatband potential. These results are compared with reaction velocities derived from extrapolation methods at millimeter-sized ZnO electrodes. It is seen that the extrapolation method is insensitive to nonideal behavior in the reducti on reaction whereas the microelectrode method is not.