INTERFACIAL BEHAVIOR OF SEMICONDUCTING RUS2 ELECTRODES - A KINETIC APPROACH

The interfacial behaviour of n-RuS2 subjected to a variety of surface treatments was investigated using rotating-disc electrode and impedance techniques. The interfacial kinetics was studied as a function of electrode pretreatment, concentration of redox species and light intensity. Heterogeneous rate constants and transfer coefficients were determined from Tafel plots obtained in the dark and under illumination and compared with values reported for platinum and RuO2. Phenomenologically, electron exchange with Fe3+/Fe2+ proceeds differently on the polished and electrochemically treated surfaces, which is supported by the determination of the surface state concentrations before and after electrochemical treatment. To support these preliminary conclusions, the kinetics of Fe3+ reduction in darkness was also analysed on the basis of a two-step charge transfer model which takes charge transfer over surface states into account. Rate constants and potential drops in the Helmholtz layer were determined using this model. For the polished electrode the applied potential drop in the Helmholtz layer is 80% and the heterogeneous standard rate constant is 6.5 x 10(-4) cm s-1. For the electrochemically treated electrode the potential drop is 60% and the rate constant is 2.7 x 10(-4) cm s-1.