National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, Japan.
Phys Chem Chem Phys. 2013 Jul 21;15(27):11494-500. doi: 10.1039/c3cp51136g. Epub 2013 Jun 10.
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.
为了理解聚合物电解质薄膜表面形貌与质子传导之间的关系，以玻璃碳（GC）、亲水 GC（H-GC）和铂（Pt）等不同基底上制备的全氟离子交换树脂 Nafion®薄膜作为催化剂层内的离聚物膜模型。原子力显微镜结合电化学（e-AFM）技术表明，质子传导随薄膜厚度的增加而降低；在 GC 基底上，当薄膜厚度小于约 10nm 时，质子传导会急剧下降，同时表面形貌也会发生显著变化。此外，经 UV-臭氧处理的 H-GC 基底上制备的薄膜比未经处理的 GC 基底上的薄膜具有更高的质子传导性。然而，对于厚度大于 20nm 的薄膜，Pt 基底上的质子传导性与 GC 基底相当；在约 5nm 厚的薄膜中观察到质子传导性下降，但仍远高于碳基底。这些结果表明，质子传导活性途径的数量和/或质子路径网络的连通性随薄膜厚度而变化。较薄薄膜的表面形貌受薄膜/基底界面的显著影响，与块状厚膜的表面形貌有根本的不同。
