STXM Study of the Ionomer Distribution in PEM Fuel Cell Catalyst Layers

A method of imaging ionomer in the catalyst layer (CL) of the catalyst coated membrane (CCM) in the proton exchange membrane (PEM) fuel cell was developed using scanning transmission X-ray microscopy (STXM). Component maps for ionomer in CL relative to the catalyst/carbon-support were obtained from STXM images at a few specifically pre-defined energies in the C 1s (on/off a peak characteristic for carbon support in the catalyst layer) and F 1s edges (on/off a peak characteristic for the fluorine in the ionomer). Comparing the different approaches, an optimized strategy to study the spatial distributions of chemical components in the catalyst layer was determined. C 1s multi-energy imaging was most informative for mapping all components of the carbon catalyst support. The F 1s maps offer a rapid and powerful way for visualization of ionomer in the catalyst layer.