| Abstract
| - We present a method to extract X-ray diffraction patterns from a multiphase system and analyze the particlesize distribution of each phase. The method is demonstrated for crystalline nanoparticles in the electrodes ofproton exchange membrane fuel cells (PEMFCs), where it is particularly useful to determine particle sizedistributions without destroying the device. The structure of the electrodes has a considerable influence onthe power and durability of a fuel cell and can be further optimized, for example with respect to the durabilityof the cell. Since the membrane electrode assembly (MEA) contains multiple and partially X-ray transparentlayers, the individual catalyst signals from the anode (platinum−ruthenium alloy) and the cathode (platinum)can be extracted from the diffraction patterns recorded of either side of the MEA using the technique presentedin this article. By analysis of the platinum (220) reflection by fitting a pseudo-Voigt function, the individualparticle size distributions are determined for the anode and the cathode. The catalyst surface area loss due toparticle growth is studied in long-term experiments during the operation of a single model cell for 2100 hand, for comparison, during the storage in different gas atmospheres (Ar, H2, and O2) for 6500 h. With respectto the single cell operation, approximately one-third of the surface is lost in the storage experiment with aslight influence from the gas atmosphere and the catalyst type. The comparison with transmission electronmicrographs shows that the size distributions have a similar shape and width but differ in absolute sizes.
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