In the present work we extend the application of identical location transmission electron microscopy (IL-TEM) to elevated electrolyte temperatures (333 K and 348 K), close to actual operating conditions of proton conducting electrolyte membrane fuel cells (PEMFCs). The feasibility of IL-TEM is demonstrated by applying a potentiostatic degradation protocol to a high surface area carbon supported Pt catalyst. The results show that under the applied conditions carbon support corrosion is dominating the degradation of the catalyst; a process that is considered to be responsible for the reported collapse of the catalyst layer in membrane electrode assembly (MEA) tests. The finding is in contrast to degradation studies performed at room temperature where upon potential cycling mainly particle coalescence was observed without visible changes in the support of the catalyst. (C) 2011 Elsevier B.V. All rights reserved.