In-Plane Distribution Of Water Inside Nafion (R) Thin Film Analyzed By Neutron Reflectivity At Temperature Of 80 Degrees C And Relative Humidity Of 30%-80% Based On 4-Layered Structural Model

Structures of polymer electrolyte membranes and binders and the distribution of water inside are important for designing new ion-conductive ionomers for polymer electrolyte fuel cells. Neutron reflectometry (NR) was carried out on a Nafion (R) film with a thickness of 100 nm formed on native SiO2 surface on Si(100) for understanding the in-plane water distribution. The temperature was set at 80 degrees C and the relative humidity at 30, 50, 65, and 80% for NR measurements, simulating the conditions for the power generation. Clear NR modulation was obtained under each condition. NR data were fit very well with a 4-layer model parallel to the substrate with different densities of Nafion and water. At the interface between the Nafion film and the Si substrate, a 1 nm water-rich layer was observed under all conditions. The water concentration increased with humidity at all 4 layers, but the thickness increased mainly at the bulk layer. (C) 2019 The Japan Society of Applied Physics