Besides high fabrication costs, degradation effects are a major drawback of high temperature proton exchange membrane fuel cells which hinder their successful commercialization so far. Detailed investigation of degradation effects is a key issue for being able to understand and prevent the occurring processes. In this work electron microscopy based methods are utilized to study the degradation of membrane electrode assemblies (MEA) that underwent different operation modes and runtimes in single cells and fuel cell stacks. One focus is placed on WO3-x based catalyst support material on the anode which is a promising electrode material to substitute the widely used high surface area carbon. Via energy dispersive X-ray measurements the elemental distribution in the MEAs before and after operation is analyzed. Instead of individual nanoparticles the Pt catalyst forms several hundred nanometer large, crystalline, 3D-networks of rod-shaped nanoparticles on the WO3-x grains. The nominal 2000 h in-situ long-term fuel cell operation tests reveal that the performance of the MEAs with WO3-x based anodes lies 10 mV below an MEA with standard high surface area carbon. However, the degradation behavior of the MEAs containing WO3-x outperforms the conventional used MEA and therefore confirms the usability of WO3-x as catalyst support. (C) 2014 The Electrochemical Society. All rights reserved.