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Journal of the Electrochemical Society, Vol.157, No.2, B256-B259, 2010
Teflon-Coated Carbon Fiber Core/Shell Structure Based Hydrophobic Gas-Diffusion Electrode for Proton Exchange Membrane Fuel Cells
Teflon-like film-covered carbon fiber fabricated using the CHF3 plasma technology as a core/shell-like structure for the hydrophobic porous gas diffusion electrode (GDE) formation is successfully demonstrated for use in proton exchange membrane fuel cells (PEMFCs). The Teflon-like film, with thicknesses up to 1200 nm, produces an optimum water contact angle (WCA) of 131 degrees, which is attributed to the superior cross-linking density and greater number of -CF2 functional groups. When compared with the film grown on a planar Si substrate, a similar WCA tendency was clearly observed; nevertheless, all of the obvious value was reduced in Delta WCA/WCA=23% due to the Lotus effect. The PEMFC measurements show that GDE with a Teflon-like film thickness of 1200 nm modules has the best performance with a maximum power density of 0.52 W/cm(2). However, cell performance tends to decline when the film thickness is increased to 2700 nm, a result which is ascribed to the great sheet resistance and Teflon-like film cracks of the GDE.
Keywords:carbon fibres;contact angle;cracks;diffusion;electrochemical electrodes;plasma materials processing;polymers;proton exchange membrane fuel cells