MEA Pt/C Cathode Catalyst Degradation during Repeated Anode Gas Exchange Cycles: In-Situ XAFS, STEM-EDS and Electrochemical Analysis

The effects of repeated start-up/shut-down cycles on degradation of Pt/C cathode catalysts in polymer electrolyte fuel cells (PEFC) were investigated by repeated anode gas exchange (AGEX) cycles. The degradation of MEA Pt/C catalysts during the AGEX cycles was examined at three different areas of the MEAs by in-situ XAFS and STEM-EDS. The steady decreases of the electrochemical surface area and ORR performance by the AGEX processes were observed. In contrast to the aspects averaged over the whole MEA areas, in-situ XAFS can provide the position-dependent structural and electronic information on Pt nanoparticles at different positions in the MEA during the AGEX cycles. The white line peak intensity in in-situ XANES spectra at Pt L III -edge decreased in the order for the MEA regions, top > bottom ≥ middle. STEM images showed that Pt particles dropped off from the carbon supporting particles in the cathode catalyst layer and large cracks and voids formed in the top area of the MEA. These aspects of the in-situ XANES spectra and STEM images are correlated with each other and the MEA degradation.