AVS 61st International Symposium & Exhibition
    Plasma Science and Technology Wednesday Sessions
       Session PS+2D-WeA

Paper PS+2D-WeA12
Surface Modification of Nafion Membranes Exposed to an atmospheric He-O2 and He-H2 Post-Discharge

Wednesday, November 12, 2014, 6:00 pm, Room 305

Session: Plasma Processing for 2D Materials, Coating, and Surface Modification
Presenter: Thierry Dufour, Université Libre de Bruxelles, Belgium
Authors: T.R. Dufour, Université Libre de Bruxelles, Belgium
D. Merche, Université Libre de Bruxelles, Belgium
H. Julie, Université Libre de Bruxelles, Belgium
R.F. François, Université Libre de Bruxelles, Belgium
Correspondent: Click to Email
Nafion is commonly used as a proton-conducting polymer membrane to separate the anode and cathode compartment of proton exchange membrane fuel cells (PEMFC) and water electrolyzers. The use of plasma based technology has contributed to lower catalyst loadings, thus decreasing the production costs. In this framework, our researches have been focused on a simple and robust technique to modify Nafion surface properties, using the post-discharge of an atmospheric RF plasma torch supplied in helium as carrier gas and H2 or O2 as reactive gas. The modifications achieved on Nafion samples have been compared with those of common polymers such as polyethylene, PVF and PTFE. Contrarily to these polymers, the Nafion presents more complex etching mechanisms, that may be correlated with the complexity of its molecular formula: (i) its hydrophobic region is a continuous semi-crystalline region which is Teflon®-like, being made up of main chain TFE segments, while (ii) its hydrophilic region (sulfonate group) allows water and proton/ion transport but can also swell and change in size and/or shape with water uptake (eventually forming a continuous network). We have already demonstrated that the chemical nature of the fragment species (ejected from the Nafion film) depends on the exposure time because the fluorinated backbone is not etched as efficiently as the perfluorovinyl ether groups terminated with sulfonate groups.

The morphological and chemical structural changes of the Nafion films during exposure to the post-discharge have been characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) as well as WCA (Water Contact Angle) measurements. Moreover, a characterization of the proton conductivity and of the methanol permeability will also be introduced.

This work is supported by PSI-IAP 7 (plasma surface interactions) from the Belgian Federal Government BELSPO agency.