The influence of intermediate characterizations used in long-term accelerated stress tests (ASTs) to monitor the changes of the electrochemically active surface area of carbon-supported Pt nanoparticles (Pt/HSAC) was investigated. Our results indicate that, in the studied experimental protocol (potentiostatic polarization at E = 1.0 V vs. RHE during 96 h), the loss of the electrochemically active surface area is greatly exacerbated by intermediate characterizations such as cyclic voltammetry or stripping of a saturated COad surface layer. These results can be understood in view of the breakdown of the passivation layer formed on the Pt/HSAC electrocatalyst during the polarization at E = 1.0 V vs. RHE. By using identical location transmission electron microscopy, the structural modifications of the Pt/HSAC nanoparticles could be monitored. The migration/agglomeration of Pt nanocrystallites, the growth of Pt nanocrystallites by electrochemical Ostwald ripening, and the corrosion of the high surface area carbon support are more pronounced when cyclic or COad stripping voltammograms are implemented in the AST. A detailed analysis of the identical-location transmission electron microscopy images also indicates that adsorbed CO molecules minor the dissolution of Ptz+ ions into the electrolyte.
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