An Epoxy-Free Sample Preparation Approach to Enable Imaging of Ionomer and Carbon in Polymer Electrolyte Membrane Fuel Cells

Performance and durability of electrodes in proton exchange membrane fuel cells (PEMFCs), as one of the most promising zero-emission power generation technologies, depend on the composition, microstructure, and distribution of its components-metal catalyst, carbon support, and ionomer. Their improvement requires an in-depth understanding of the electrodes' structure-property-performance relationship, for which transmission electron microscopy (TEM) has been an invaluable tool. However, the conventional TEM sample preparation, namely epoxy-embedding ultramicrotomy, poses impediments in imaging ionomer and distinguishing it from carbon. Therefore, in this research, an epoxy-free ultramicrotome technique is implemented on beginning-of-life (BOL) and end-of-life (EOL) PEMFC samples. For the first time, TEM and electron tomography-TEM images reveals fascinating details of the ionomer network, carbon particles' structure, and Pt distribution in BOL, as well as their structural changes after the cell degradation. Finally, the structural descriptors, extracted by a proprietary quantification method, are correlated with visual observations.