Platinum catalyst dissolution with subsequent reduction and deposition of Pt particles in the membrane can lead to a significant loss of polymer electrolyte fuel cell (PEFC) performance. To quantify the amount of deposited platinum, a novel transmission electron microscopy (TEM) sectioning method was employed. This method was used to visualize, count and size Pt particles in a defined volume of the membrane, thus allowing the calculation of the deposited Pt mass. After potential cycling between 0.6 V and open circuit voltage, a Pt particle band was formed in the middle of the membrane containing 16% of the initial cathode Pt loading. Start/stop cycling was found to result in deposition of Pt particles both close to the cathode (3% cathode Pt loss) and the anode catalyst layer (1% anode Pt loss). TEM sectioning allowed for the separation of Pt surface area losses caused by deposition in the membrane and particle growth in the catalyst layers. Particle growth was the dominating surface area loss mechanism after potential cycling and start/stop cycling. Using TEM sectioning, the Pt surface area in the membrane was also accessible, which is a crucial parameter for membrane degradation. (C) 2011 Elsevier B.V. All rights reserved.