Effects of Repeated Feed-Gas Exchange Processes on Degradation Processes of Pt-Based PEFC Cathode Catalysts Studied by In-situ XAFS, STEM-EDS and Electrochemical Methods

Repeated anode gas exchange (AGEX) cycles and cathode gas exchange (CGEX) cycles were applied to MEAs with Pt₃Co/C cathode catalysts to investigate the degradation processes and to compare with the case of Pt/C. The structural and electronic changes of the catalysts during the feed gas-exchange cycles were examined at the top position area of the MEAs by in-situ XAFS and at the top and bottom positions by STEM-EDS. The ORR performance decreased steadily by the AGEX cycles though STEM revealed neither large cracks nor voids nor detached particles in the top position area of the MEA by the AGEX cycles where the electrochemical surface area (ECSA) remained unchanged. On the other hand, neither ORR performance nor ECSA decreased by the CGEX cycles though the particle size only in the bottom position area increased a little after the CGEX treatment. In-situ time-resolved XAFS spectra at Pt L_III-edge showed a decrease of the XANES white line peak height in case of the AGEX, which is not due to particle growth.