We demonstrate that an electrolyte probe can be used to measure the difference in oxygen chemical potential across the surface, when an oxygen flux is forced through an oxygen permeable membrane disk. The oxygen flux as well as the total oxygen chemical potential difference is carefully controlled by an oxygen pump. The developed method is tested on a (La0.6Sr0.4)0.99Co0.2Fe0.8O3−delta membrane. An La0.75Sr0.25MnO3/Y0.16Zr0.84O1.92/La0.75Sr0.25MnO3 oxygen pump was attached to one side of the membrane. A conical Ce0.9Gd0.1O1.95 (CG10) electrolyte probe was pressed against the other side of the membrane. The voltage difference between the base and the tip of the CG10 probe was recorded with an applied oxygen flux through the membrane. This voltage was used to extract precise values of the surface exchange rate constant, kO. Using these values of kO, the vacancy diffusion factor, Dv0, could be extracted from data of the flux and the oxygen chemical potential difference across the membrane measured with the oxygen pump. Furthermore, upon a gas change, the transient voltage signals of the oxygen pump and the probe could be fitted to give values of Dv0 and kO.
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