We discovered a metallic Pt–Co alloy band in the electrolyte region of 300–400 nm from the cathode edge and square planar Pt 2+–O 4 species and octahedral Co 2+–O 6 species in the area between the cathode edge and the Pt–Co band.
The MEA Pt 3Co/C after 10,000 ADT-rec cycles had many cracks and pores in the cathode electrocatalyst layer, and about 90% of Co had been dissolved and removed from the cathode layer. It was also shown that its existence suppressed the oxidation and dissolution of Pt. It was shown that Co dissolved in the electrolyte region had an octahedral Co 2+–O 6 structure, based on a 150 nm × 150 nm nano-XAFS analysis. In contrast, there was no correlation between the size or Co/ionomer ratio of the cracks and pores and the Co dissolution of the MEA Pt 3Co/C. The larger the size of the cracks and pores in the MEA Pt/C and the smaller the ratio of Pt/ionomer of cracks and pores, the faster the rate of catalyst degradation. In contrast, Co oxidized and dissolved over a wide range of the cathode layer (∼70% of the initial Co amount). In the MEA Pt 3Co/C, after 5000 ADT-rec (rectangle accelerated durability test) cycles, unlike the MEA Pt/C, there was no oxidation of Pt. Nano-X-ray absorption fine structure (XAFS)/Scanning transmission electron microscope (STEM)-energy dispersive X-ray spectroscopy (EDS) technique that we developed to elucidate durability factors and degradation mechanisms of a MEA Pt 3Co/C cathode electrocatalyst with higher activity and durability than a MEA Pt/C.
In order to obtain a suitable design policy for the development of a next-generation polymer electrolyte fuel cell, we performed a visualization analysis of Pt and Co species following aging and degradation processes in membrane-electrode assembly (MEA), using a same-view.
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