Tomographic Analysis of Polymer Electrolyte Fuel Cell Catalyst Layers: Methods, Validity and Challenges
The precise morphology of all phases within a CL plays a key role for reactant transport and thus performance: Platinum catalyst particles with poor connection to ion conducting, electron conducting or gas transporting phases cannot contribute to the fuel cell reaction. Also, the precise shape of the pathways of the reaction species determines their effective transport properties. Wetting or non-wetting pore wall areas influence water precipitation and therefore the generation of liquid water networks. Such networks both improve ionic transport and adulterate gas transport.
Facing the tremendous influence morphology has on PEMFC performance, cost and durability, tools to image morphology are an obvious necessity. While there is a variety of imaging methods that allow three-dimensional reconstructions, only few are able to resolve the nanostructure of CLs: x-ray tomography (Xt), focused ion beam / scanning electron microscopy tomography (FIB-SEMt) and transmission electron microscopy tomography (TEMt) .
Both Xt and FIB-SEMt have been proven to enable differentiating porous and solid phase within PEMFC CLs [2,3]. TEMt allows imaging with resolutions below 1 nm and can be directly used to image Platinum particles . To image all important phases multiple tomographic techniques must be used. In this talk we give an overview on the latest tomographic analysis techniques for PEMFC CL reconstruction with a particular emphasis on FIB-SEMt, multi-scale imaging approaches and validity of the existing reconstruction methods.
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