Highly Oriented Sulfonic Acid Groups in a Nafion Thin Film on Si Substrate

• Published in: Journal of physical chemistry. C Vol. 117; no. 7; pp. 3294 - 3297
• Main Author: Nagao, Yuki
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 21.02.2013
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; Polymeric membrane; Tetrafluoroethylene polymer; Spin-on coatings; Proton conductivity; Density functional method; Infrared spectrum; Vibrational mode; Sulfonic acid; Fuel cell; Thin film; Hydrogen bond
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp311622p

Solid state ionics is a research field attracting much current attentions because of the ideal power sources for use with portable electronic devices having high power-to-weight ratios. One of the most urgent subjects in this field is to understand proton transport properties at the interface between inorganic materials and polymer electrolyte from the viewpoint of developing much more powerful energy. In this study, a 150-nm-thick Nafion thin film was prepared by spin-coating on a silicon (Si) substrate to investigate the proton transport property at the interface. The infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (p-MAIRS) technique was applied to investigate the in-plane (IP) and out-of-plane (OP) spectra to the surface. The IP spectrum showed a well-known spectrum, but the OP spectrum was quite different from the IP spectrum. An anomalous IR peak was observed in the OP spectrum at 1260 cm–1. From density functional theory (DFT) calculations, this peak was attributed to the −SO3H vibration modes between two sulfonic acid groups with hydrogen bonds. These results demonstrate that the Nafion thin film on Si substrate had a highly oriented structure with the sulfonic acid groups at the side chain. Impedance measurements of Nafion thin film were conducted to investigate the proton transport property of the Nafion thin film on SiO2 substrate. The proton conductivity of the thin film exhibited a lower value than that of the commercial Nafion membrane. The low proton conductivity of the Nafion thin film was related with these highly oriented structures.