Local Activation and Degradation of Electrochemical Processes in a SOFC

The local electrochemistry is studied in a SOFC repeat-element using a test setup that allows a local control of the polarization. During long-term tests, the local current densities evolve, following activation and degradation periods. Electrochemical impedance spectroscopy (EIS) measurements performed at regular intervals are used to analyze the activation and degradation of the individual electrochemical processes. By computing the distribution of relaxation times (DRT) from the EIS spectra, a total of 6 electrochemical processes are revealed and their evolution studied separately. It is found that not only the activation/degradation rates but also their spatial evolution are strongly influenced by the choice of materials and by the operating conditions. In particular, the degradation of the anode propagates over the active area with important local differences, and in a wave-like manner that differs from one test to the other. Results are presented and analyzed for several long-term tests operated with hydrogen or steam-reformed methane as fuel.