title: Effect of interface on surface morphology and proton conduction of polymer electrolyte thin films.
abstract: To understand the relationship between surface morphology and proton conduction of polymer electrolyte thin films, perfluorinated ionomer Nafion® thin films were prepared on different substrates such as glassy carbon (GC), hydrophilic-GC (H-GC), and platinum (Pt) as models for the ionomer film within a catalyst layer. Atomic force microscopy coupled with an electrochemical (e-AFM) technique revealed that proton conduction decreased with film thickness; an abrupt decrease in proton conductance was observed when the film thickness was less than ca. 10 nm on GC substrates in addition to a significant change in surface morphology. Furthermore, thin films prepared on H-GC substrates with UV-ozone treatment exhibited higher proton conduction than those on untreated GC substrates. However, Pt substrates exhibited proton conduction comparable to that of GCs for films thicker than 20 nm; a decrease in proton conduction was observed at ∼5 nm thick film but was still much higher than for carbon substrates. These results indicate that the number of active proton-conductive pathways and/or the connectivity of the proton path network changed with film thickness. The surface morphology of thinner films was significantly affected by the film/substrate interface and was fundamentally different from that of the bulk thick membrane.
authors.affiliation: National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, Japan. a-oohira@aist.go.jp
authors.forename: Akihiro
authors.initials: A
authors.lastname: Ohira
authors.forename: Seiichi
authors.initials: S
authors.lastname: Kuroda
authors.forename: Hamdy F M
authors.initials: HF
authors.lastname: Mohamed
authors.forename: Bruno
authors.initials: B
authors.lastname: Tavernier
mesh_terms: D002244:Carbon / Q000737:chemistry; D055664:Electrochemical Techniques; D004573:Electrolytes / Q000737:chemistry; D005465:Fluorocarbon Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D010316:Particle Size; D010984:Platinum / Q000737:chemistry; D011522:Protons; D013499:Surface Properties
chemical_list: D004573:Electrolytes; D005465:Fluorocarbon Polymers; D011522:Protons; C040402:perfluorosulfonic acid; D010984:Platinum; D002244:Carbon