Co oxidation accompanied by degradation of Pt-Co alloy cathode catalysts in polymer electrolyte fuel cells

The electronic structure of Co ions in Pt3Co alloy cathode catalysts for polymer electrolyte fuel cells (PEFCs) under different operation conditions has been investigated using X-ray absorption spectroscopy (XAS). The line shapes of the Co 2p XAS spectra indicate that the Co atoms in the cathode layer are predominantly metallic in all cells, and the spectrum of the first-operated cell is the most metallic among them. The Co 2p XAS spectra slightly change depending on the operation conditions, and the differences in the spectra can be explained by the presence of cobalt oxides. Decomposition analysis of the Co 2p XAS spectra reveals that the operation of Pt-Co PEFCs yields trivalently oxidised cobalt in the cathode layer.