A kinetics-based approach to the steady-state and impedance response of photoelectrodes

A kinetics-based analytical model is developed to describe the steady-state and impedance response of photoelectrodes in the case where charge carrier build-up modifies the potential distribution across the semiconductor-electrolyte junction. The predictions of the steady-state model are compared with numerical calculations. It is shown that carrier build up should accelerate interfacial hole transfer by increasing the potential drop across the Helmholtz layer. This effect may explain observations of higher reaction orders with respect to hole concentration during photoelectrochemical oxygen evolution. The analytical model is extended to photoelectrochemical impedance spectroscopy (PEIS). The calculations indicate that interpretation of PEIS measurements becomes more complicated if high illumination intensities are used. The modeling of the analytically calculated PEIS response using equivalent circuits is discussed with the aim of understanding the physical significance of the resistive and capacitive elements.