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P: Plasmaphysik
P 4: Diagnostik 1; Niedertemperaturplasmen / Plasmatechnologie 2; Magnetischer Einschluß 2
P 4.17: Poster
Monday, March 27, 2006, 17:00–19:00, Flure
Characterization of plasma modified membranes for fuel cells — •S. Enge, M. Walker, A. Schulz, and U. Stroth — Universität Stuttgart, Institut für Plasmaforschung, Pfaffenwaldring 31, D-70569 Stuttgart
Fuel cells are providing an efficient way to convert chemical energy into electric energy. For portal applications polymer electrolyte membrane (PEM) fuel cells are the best choice. A direct methanol fuel cell (DMFC) uses methanol instead of hydrogen as fuel. So the energy density of the system is increased. The permeation of methanol through the PEM leads to losses of methanol and to a reduction of the cell voltage. The lack of contact between the membrane and catalyst reduces the achieved cell voltage too. A plasma induced modification of the membrane surface is investigated in terms of methanol permeation and surface energy for Nafion 105 and some new fuel cell membranes. For the plasma induced surface modification, a low pressure microwave plasma source the Duo-Plasmaline powered with 2 x 1.2 kW at 2.45 GHz was used. The modifications were done with O2, N2 and CF4 plasmas. Time dependent methanol permeation measurements and simulations were done on Nafion 105 and several crosslinked blend membranes. It could be observed that the diffusion coefficient is exponential dependent on the methanol concentration. The new surface energies are investigated by the sessile drop method, with four test liquids. To investigate the formed molecular groups in the membrane with transmission FTIR, thin films of the polymer were prepared on molybdenum mirrors, improving the ratio of the signal from the surface to signal from the volume.