Understanding the ionomer structure and the proton conduction mechanism in PEFC catalyst layer: Adsorbed Nafion on model substrate
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To understand the structure/property of the ionomer in the CL, adsorbed Nafion thin films were prepared on model substrate, SiO 2 terminated silicon wafer, by spontaneous adsorption of Nafion from its 0.1 to 5 wt% solution. Fitting of Variable Angle Spectroscopic Ellipsometry (VASE) data yielded thickness of adsorbed films ranging from 4 nm at low concentrations (0.1 wt% film) to 306 nm at high concentrations (5wt% film). Contact angle measurements indicated that the low (0.1 wt%) and high (3 wt%) films to posses hydrophobic surface but the intermediate concentration (0.5 wt% and 1.0 wt%) film surface to be hydrophilic. Conductivity measurements of adsorbed films over a range of RH showed that all films prepared from 1 wt% and lower concentrations solutions to possess similar conductivities at high RH. However, the 5wt% film showed much higher conductivity indicating a different proton conduction mechanism for low and high concentration films. © 2011 ECS - The Electrochemical Society.