Quantitative in Situ Analysis of Ionomer Structure in Fuel Cell Catalytic Layers.

A quantitative in situ investigation of the structure of the catalytic layer of polymer electrolyte membrane fuel cells using material-sensitive and conductive atomic force microscopy is reported. The distribution and size of the ionomer phase at the surface of the catalytic layer is retrieved from adhesion force mappings, measured at high humidity and up to 75 °C. The average ionomer layer thickness varies between 7 and 13 nm for three differently prepared samples, as concluded from the histograms. Evidence of a lamellar structure of the thinner ionomer layers is presented. A significant thinning of the ionomer layers after long-term fuel cell operation is observed.