Interesting that if we take an electrolyte membrane made of CeO2-based electrolyte, rather thick, for example about 0.8-1.0 mm or even thicker, we anyway in SOFC mode will observe the OCV value lower that that for pure ionic conductor. However the layer of the reduced ceria with a mixed conductivity we have only on the anode side, and this layer, according to different sources, is very thin compared to the membrane thickness (it can be 5-20 mkm) Why such a thick layer of non-reduced ceria, which is pure ionic conductor does not block electronic current? if we apply another ionic conductor as a buffer layer at the cathode (Bi2O3 based electrolyte, for example) its thickness of 20 mkm, again according to the literature, may be enough to eliminate the internal short circuing in the cell and reach high OCV values.
Hi Lene ;)
Really this question has to be reasked next: "What is difference between ceria-based electrolytes and zironia based ones?". Ansver is "surface phase transition"
See:
Shkerin, S.N., Izv. Akad. Nauk, Ser. Fiz., 2002, vol. 66, p. 890, or
Chapter The YSZ Electrolyte Surface Layer: Existence, Properties, an...
The same phenomenon exists for ceria but really weak. It dissapears about 400 C.
For YSZ nearsurface layer exists up to 1070 C.
]So, when electrode processes are investigated at 1100 C [Article Кинетика реакции на модельном электроде в системе O2,Pt/O2- ...
it is exactly the same case as for ceria-based electrolytes.
At low temperature a zirconia-based electrolyte really is composite of two materials. One of its is low-conductive but "strong" layer. This is reason of high ionic transfer number for YSZ.
By way, it is similar case of Li-ion batteries where electrolyte is "SEI at negative electrode | liquid electrolyte | SEI at positive electrode". It is just composite electrolyte
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