Identical locations transmission electron microscopy study of Pt/C electrocatalyst degradation during oxygen reduction reaction

► This study has demonstrated the use of the identical locations transmission electron microscopy (IL-TEM) method with the TEM grid as the sole working electrode. This configuration allowed a direct correlation to be made between the electrochemical response and the TEM analysis. ► Our observations provide the first direct, microscopic evidence of a reduction in particle size for C-supported Pt catalysts under ORR conditions after potential cycling simulating start-up and shutdown of a fuel cell ► These results provide strong evidence to suggest that Pt dissolution is the dominant mechanism of catalyst degradation during fuel cell operation.