The Oxygen Reduction Kinetics of Mixed Conducting Electrodes: Model Considerations and Experiments on La0.6Sr0.4Co0.8Fe0.2O3 Microelectrodes

A model is presented that yields current-voltage relations for electron transfer reactions at the electrode/gas interface of mixed conducting electrodes. The approach introduced appears necessary since the relevant electrostatic potential step at the gas/solid interface is not equivalent to the applied overpotential. As a consequence, surprising features such as an additional factor of two in the exponents of the current-voltage (I-V) relation or limiting currents even if charge transfer is the rate determining step are deduced depending on adsorption site concentration, type and equilibrium concentration of adsorbed surface species, etc. Experiments with well-defined La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 microelectrodes on yttria-stabilized zirconia electrolytes were performed to investigate the mechanism of the oxygen reduction reaction. A comparison of the measured I-V characteristics with the model calculations suggests that the electron charge transfer to an adsorbed O ad atom is the rate limiting step of the corresponding reduction reaction. Further measurements, however, are required to verify this conclusion.