Ionomer Thin-Film Network in PEFC:The Impact of Interface on Mass Transport

摘要

An ionomer is a binder of a catalyst layer (CL), that covers the carbon (C)supported platinum (Pt)catalyst nanoparticles (NP)with a nanometer thin-film. High proton conductivity and high oxygen permeability are required for an ionomer in a cathode CL that also is one of the keys for high-performance and high-durability of polymer electrolyte fuel cells (PEFC). Studies using a model ionomer thin film on Pt and/or carbon electrodes have reported that proton conductivity and gas permeability differ from the bulk membrane. Here, interfaces inside CL are reproduced by coating ionomer thin films (2-10nm)on a surface consisting of various surface areas of Pt-NPs (2-3nm)embedded in amorphous C (40nm)films. A remarkable reduction of the proton conductivity in a thin film thinner than 5nm confirmed the difference with the bulk. We also found that the changes of morphology and proton conduction significantly depend on the ratio of the Pt/C surface area. These results suggest that the hydrous behavior in the ionomer thin film is altered, which could be affecting the amount of protons transported inside the thin film.