Degradation of the Pt/C Electrode Catalyst Monitored by Identical Location Scanning Electron Microscopy during Potential Pulse Durability Tests in HClO4 Solution

The degradation of Pt nanoparticles in the Pt/C electrode catalyst of PEFC (polymer electrolyte fuel cell) during a potential pulse durability test was investigated using identical location field emission scanning electron microscopy (IL-FE-SEM). The degradation was classified as disappearance, migration, precipitation, coalescence, transformation, or other processes, although the size of most particles changed. Furthermore, several combinations of consecutive degradation were first observed. Thus, the IL-FE-SEM observations allowed us to discuss the degradation mechanism semi-quantitatively. Disappearance was recognized if the particle was not observed at the original position or a neighboring position and the frequency of this phenomenon reached a maximum of 10%. Migration was recognized if the particle moved from its original position to a neighboring position. The frequency of migration increased to 10% after the 2,000th pulse, then decreased up to the 5,000th pulse, and increased again after further pulses. Precipitation was observed at a frequency that reached 4% after the 5,000th pulse. Interestingly, migration and transformation were observed to occur following precipitation of Pt particles. Coalescence following migration was found to be a comparatively minor phenomenon. Transformation was the major phenomenon recognized in this study and was frequently observed following coalescence or precipitation of Pt particles. (C) The Electrochemical Society of Japan, All rights reserved.