Sublayered Structures of Hydrated Nafion® Thin Film Formed by Casting on Pt Substrate Analyzed by X-ray Absorption Spectroscopy under Ambient Conditions and Neutron Reflectometry at Temperature of 80°C and Relative Humidity of 30–80

• Published in: Denki kagaku oyobi kōgyō butsuri kagaku 2019/09/05, Vol.87(5), pp.270-275
• Main Authors: KAWAMOTO, Teppei, AOKI, Makoto, KIMURA, Taro, CHINAPANG, Pondchanok, MIZUSAWA, Takako, YAMADA, Norifumi L., NEMOTO, Fumiya, WATANABE, Takeshi, TANIDA, Hajime, MATSUMOTO, Masashi, IMAI, Hideto, MIYAKE, Junpei, MIYATAKE, Kenji, INUKAI, Junji
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; Air temperature; Binders; Catalysts; Computer simulation; Electric power generation; Electrolytes; Electrolytic cells; Humidity; Ionomers; Nafion Thin Film; Neutron Reflectometry; Platinum Substrate; Polymers; Pressure; Proton exchange membrane fuel cells; Reflectometry; Relative humidity; Silicon dioxide; Spectrum analysis; Substrates; Temperature effects; Thickness; Thin films; Water distribution; Water engineering; Water uptake; X ray absorption; X-ray Absorption Spectroscopy; X-ray spectroscopy
• ISSN: 1344-3542; 2186-2451
• DOI: 10.5796/electrochemistry.19-00042

The structures of polymer electrolyte membranes and catalyst layer binders and the distribution of water therein are important for designing new ion-conductive ionomers for polymer electrolyte fuel cells. To aid the understanding of the in-plane water distribution, neutron reflectometry (NR) was carried out on a Nafion® film with a thickness of 150 nm formed on a 20-nm Pt layer deposited on Si(100) with a native SiO2 layer. By means of ambient pressure X-ray absorption spectroscopy at room temperature in air, the Pt substrate was found to be metallic. For NR, the temperature was set at 80°C and the relative humidity at 30, 50 and 80%, simulating the conditions for power generation. Clear NR modulation was obtained under each condition. NR data were fit very well with a 3-sublayered model parallel to the substrate with different densities of Nafion and water. The influence of the Pt substrate was observed not only at the Nafion/Pt interface, but also on the thin-film structure. The water uptake in a Nafion film on Pt also differed from that on SiO2. At 80°C, the surface of the Pt substrate was proposed to be oxidized, and the Nafion/Pt interface was found to contain water, in contrast to the interface observed at room temperature.