Understanding the Nafion-Pt interface structure is important because fuel cell reactions occur at the three-phase boundary. Infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (p-MAIRS) technique was used to investigate the in-plane (IP) and out-of-plane (OP) spectra in the identical substrate. Our previous study revealed that the proton conductivity of the Nafion thin films decreased at the MgO and SiO2 surfaces. We proposed that the origin for the lower proton conductivity can be derived from the highly oriented structure at the interface. However, the interface structure of the Nafion-Pt interface remains unclear. In this study, Nafion thin films were prepared by spin-coating on a Pt-deposited MgO substrates. The IP spectrum exhibited a well-known spectrum, but the OP spectrum was quite differed considerably from the IP spectrum. Furthermore, thickness dependence of the degree of orientation for this OP band was observed at the Nafion-Pt interface. This OP band can be assigned as the vibration mode of the mixture of the CF2 and sulfonic acid groups. At the low-RH region, proton conductivity of the Nafion thin film on the Pt-deposited surface was 1 order of magnitude higher than that on the SiO2 surface. Furthermore, the activation energy was 0.4-0.5 eV, which is lower than that of the SiO2 surface. These results, which suggest that the Pt surface influenced the proton transport property of Nafion thin film, can contribute to understand the relationship between the proton transport property and thin film structure on the Pt-deposited surface at the three-phase boundary for fuel cells.

Fast proton conduction was achieved in organized lamellar structures with in-plane oriented structure parallel to the substrate surface using a lyotropic liquid-crystalline (LC) property. Alkyl sulfonated polyimides (ASPIs) with bent main chain structure were newly synthesized to investigate relations between the higher order structure and proton transport properties. Proton conductivity of all polyimide thin films was greater than 10–2 S/cm. Grazing-incidence small-angle X-ray scattering (GI-SAXS) revealed that both planar and bent ASPI thin films exhibited humidity-induced lyotropic lamellar structure. Infrared p-polarized multiple-angle incidence resolution (pMAIR) studies revealed that main chain backbones of both planar and bent ASPI thin films show an in-plane orientation parallel to the substrate surface. Results demonstrate that sulfonated alkyl side chains contribute strongly to the lyotropic LC property, which enhances molecular orderings and proton conductivity by water uptake. This study extends knowledge of the molecular design for highly proton conductive polymers with humidity-induced lyotropic LC property.

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A lack of knowledge about the features of Nafion confined to ultrathin films at the interface has motivated additional examinations to promote the performance of polymer electrolyte membrane fuel cells (PEMFCs). In this work, we demonstrated the utilization of practical film-forming technique inkjet printing to fabricate a Nafion ultrathin film less than 10 nm thickness. However, the well-known "coffee-ring" effect caused poor quality of the printed pattern, which has restricted its application. This report describes a systematic investigation of necessary parameters such as ink concentration, substrate type, pitch, and offset for printing processes. Furthermore, post-treatment in an ethanol vapor atmosphere exhibited a significant effect on flattening and homogenizing the film surface morphology. Results show that the well-distributed Nafion ultrathin film modified by ethanol vapor annealing manifested much-improved proton conductivity.

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