IMPEDANCE MEASUREMENTS ON OXYGEN REDUCTION REACTION IN MOLTEN CARBONATE

To elucidate the oxygen reduction in molten carbonate the process is studied by means of impedance measurements. On the basis of the super oxide mechanism a theoretical impedance model has been developed. It consists of a charge transfer resistance, a Warburg impedance and a Gerischer or homogeneous reaction impedance. The latter is due to the recombination reaction of oxide with carbon dioxide forming carbonate. This model also holds for the peroxide mechanism apart from a different dependency on the oxygen and carbon dioxide partial pressure. The impedance data measured on a flat electrode in a half cell for several gas mixtures were fitted according to this model under the assumption that only one mechanism, the peroxide or super oxide mechanism, dominates the reaction. The measured dependency of the various elements in the model on oxygen and carbon dioxide partial pressure do not fully agree with the theoretical expected dependency. This might be due to the fact that neither one of the mechanism predominates in the melt, but both occur simultaneously.