Einsatz von Niederdruck-Mikrowellen-Plasmen für die Oberflächenmodifikation und Erzeugung von Diffusions-Barrieren auf Brennstoffzellen-Membranen [article]

Jochen Feichtinger, Universität Stuttgart, Universität Stuttgart
2004
In the presented work the methanol permeability of different polymer-electrolyte-membranes (PEM) that are used in direct methanol fuel cells (DMFC) is characterised and different approaches are discussed, how the application of low-pressure microwave plasmas can help to improve the surface- and permeation-properties of such membranes. The polymer membrane is the most important part in a DMFC and has two main functions, the first is the transport of protons from the anode to the cathode and the
more » ... he cathode and the second is the separation of the anode and cathode parts of the fuel cell. Due to electro-osmotic drag water molecules are transported together with the protons to the cathode. Because of the good solubility of methanol in water methanol molecules also permeate from the anode to the cathode. This undesired so called methanol-crossover limits the efficiency of state-of-the-art DMFCs. The simulation presented in section 3.3 that was calculated at the IWV-3 at the Forschungszentrum Jülich proves that a reduction of the methanol permeability by a factor of 10 leads to an improved DMFC efficiency by a factor of 2 if the proton conductivity of the membrane is not negatively affected. Therefore two possibilities were investigated to reduce the methanol permeability of DMFC membranes by the application of low-pressure microwave plasmas. To measure the effect of the barrier concepts an experiment was designed to measure the time resolved absolute methanol flux across the membrane material (see chapter 5). Due to the strong water uptake and swelling of the membrane materials the diffusion coefficient of the membrane is a function of the methanol concentration. Finite-element-simulation was used to simulate the methanol permeability of the membranes. Additionally to the state-of-the-art Nafion membrane an acid-base blend membrane that was developed at the ICVT of the University Stuttgart was characterised. The diffusion coefficient of the innovative membrane material is 60 times less than the one of Nafion. With the Duo-Plasmaline plas [...]
doi:10.18419/opus-1634 fatcat:xuiuhrbo2fbr5ngrzdhjyejvse