Electron Transfer at the Metal Oxide/Electrolyte Interface: A Simple Methodology for Quantitative Kinetics Evaluation

While quantitative models exist for measuring rate constants for electron exchange at the surface of semiconductors to or from redox couples in solution, their use is very limited for studying transition metal oxide electrodes. Taking advantage of the possibility of tuning the doping level of WO3 by thermal treatment, we measured the rate constants for electron injection from soluble probes in the so-called reverse mode. Hence, we could demonstrate that intermediate states located below the conduction band take part to the oxidation process and that the rate constant is bimolecular with a first order dependence on the concentration of redox probes and the concentration of intermediate states. A kinetics model was thereby developed to describe this reverse mode and a zone diagram established, which can then be used to quickly assess rate constants for interfacial electron transfer on the surface of transition metal oxides semiconductors that are critical for applications such as solar energy conversion.