In-Situ XAFS Study to Monitor the Degradation of an Fe/N/C Cathode Catalyst in PEMFC

Abstract

Understanding the degradation mechanism of Fe/N/C cathode catalysts in proton exchange membrane fuel cells (PEMFCs) is extremely important. In this study, an Fe/N/C catalyst prepared from polyimide nano-particles were placed in an in-situ cell for X-ray absorption spectroscopy, and its Fe K-edge adsorption spectra were recorded during a continuous operation of the fuel cell. The Fe/N/C catalyst used in this study was prepared by pyrolyzing Fe-containing polyimide nano-particles, which were synthesized by the precipitation polymerization of Pyromellitic dianhydride and 1,3,5-tris(4-aminophenyl)benzene. The Fe content after the preparation procedure was 0.6 wt%. This catalyst was used to fabricate a membrane and electrode assembly (MEA) with a Pt/C anode and a Nafion 212 membrane. This MEA was installed in a test cell for in-situ X-ray adsorption fine structure (XAFS) measurements, and operated at 0.5 V and 80°C for 8 h monitoring its Fe K-edge adsorption spectra. Fig. 1 shows the changes in the spectra during the fuel cell operation. The valence of the Fe specie at the initial stage was 3+. The spectra gradually changed during the fuel cell operation, suggesting that the dissolution of the Fe species from the active sites. This change could be relevant to the degradation of the cathode catalyst. Acknowledgements This study is financially supported by NEDO. The in-situ XAFS study was carried out at BL36XU in SPring-8 (No. 2016B7907, 2018A7840 and 2018B7907). Figure 1