In situ Methods for Analysis of Polymer Electrolyte Membrane Fuel Cell Materials by Soft X-ray Scanning Transmission X-ray Microscopy

The performance, efficiency and lifetime of polymer electrolyte membrane fuel cells (PEM-FC) is a function of the composition and nanostructure of the electrodes. Optimization of these properties is critical, in particular for the cathode where the rate limiting oxygen reduction reaction takes place. For the past 5 years we have used soft X-ray scanning transmission X-ray microscopy (STXM) to study a wide range of issues in PEM-FC optimization [1-5]. Most of these studies have been carried out on dry, microtomed samples at ambient temperature (25 C, 0 % RH) which are very different from the typical operating conditions of the PEM-FC materials (70 C, 80 % RH). It is known that there are significant changes to the nanostructure with temperature and between dry and hydrated conditions. Thus instrumentation and methods to examine focused ion beam (FIB) or microtomy thin sections of PEM-FC membrane electrode assemblies (MEA) under more realistic conditions is needed. The in situ approach would be used to control water saturation in cathode and membrane, apply temperature changes and visualize the response of the PEM-FC materials in freeze-thaw cycling. The ability to change the sample environment in situ while examining the consequences will give added value to STXM investigations of PEM-FC. In situ STXM can be applied to many other areas of science, such as aerosol research [6].