Dictating Pt-based Electrocatalyst Performance in Polymer Electrolyte Fuel Cells; from Formulation to Application

In situ electrochemical diagnostics designed to probe ionomer interactions with platinum and carbon were applied to relate ionomer coverage and conformation, gleaned from anion adsorption data, with O2 transport resistance for low loaded (0.05 mgPt cm-2) platinum supported Vulcan carbon (Pt/Vu) based electrodes in a polymer electrolyte fuel cell. Coupling the in situ diagnostic data with ex situ characterization of catalyst inks and electrode structure, the effect of ink composition is explained by both ink-level interactions that dictate electrode microstructure during fabrication, as well as the resulting local ionomer distribution near catalyst sites. Electrochemical techniques (CO displacement and AC impedance) show that catalyst inks with higher water content increase ionomer (sulfonate) interactions with Pt sites without significantly affecting ionomer coverage on the carbon support. Surprisingly, the higher anion adsorption is shown to have a minor impact on specific activity, while exhibiting a co...