Influence of Stack Materials on the Electrochemical Performance of Anode Supported SOFC Single Cells

In planar SOFC stacks with ferritic interconnects and anode substrate-supported SOFC cells degradation is still too high for stationary applications. Determination of the sources of this degradation is difficult due to the complexity of the stacks. Methods for separating detrimental influences under conditions closely resembling stack operation and environment must be developed. Using an inert cell housing with exchangeable inserts at the electrodes provides an opportunity to selectively place stack materials close to the cathode. Results from these measurements show a clear poisoning of the cathode by chromia from the ferritic steel. Degradation rates above 20% in 1000 hours are observed for Crofer22APU-1st (first commercial batch) despite the formation of chromium manganese spinel oxide layer on the surface of the steel that reduces the release of chromium species from the steel. Coating the steel with contact layer material on average reduces the degradation rate close to 0% for the first 600 hours. After prolonged operation for 1800 hours a noticeable degradation can be observed for cells exposed to coated steel. The mechanism of the chromia retention by the contact layer is not yet clear.