Quantitative Mapping of Ionomer in Catalyst Layers by Electron and X-ray Spectromicroscopy

Quantitative mapping of ionomer in polymer-electrolyte membrane fuel cell (PEM-FC) cathodes, and associated radiation damage was studied by electron and X-ray microscopies. Mapping and damage quantification was performed by F K-a fluorescence mapping using a high-performance energy dispersive spectroscopy (EDS) detector in a scanning transmission electron microscope (STEM-EDS), and by F 1s X-ray absorption spectromicroscopy in a scanning transmission X-ray microscope (STXM). STXM was used to quantitatively analyze both STEM-EDS and STXM damage. The results show that STXM can provide ionomer maps with satisfactory quality and negligible radiation damage while STEM-EDS mapping causes significant fluorine loss. Radiation damage transforms PFSA into a disordered, fluorine depleted material.