(546e) Near Net-Shape Fabrication of Nafion® Membranes for Fuel Cell Applications

Nafion® is the foremost material used in polymer electrolyte membrane fuel cells, valued for its thermal and chemical stability, ionic properties, and mechanical strength. The properties of Nafion® can be modified by making changes to the chemical structure, by altering the membrane formation or processing procedures, or by the addition of filler materials. In this experiment, two of the three are investigated. Nafion® membranes are formed via near net-shape manufacturing (NNSM). NNSM provides a solid state route of membrane formation that bypasses many of the difficulties associated with solution and melt processing of Nafion®. This process is also used for the addition of a proton conducting ceramic to the Nafion® to create composite membranes.

Membrane formation begins with Nafion® pellets in the hydrolyzed form. These are ion exchanged with tetrabutylammonium hydroxide (TBAOH) to create a melt-processable form of the ionomer[1]. Powders are created from the Nafion® TBA+ pellets by mechanical milling at cryogenic temperature. Milled powder is then mechanically pressed to form transparent membranes of optical clarity comparable to commercial Nafion®. These are then converted back to hydrolyzed form for testing. Previous work has indicated that hot isostatic pressing (HIP) of Nafion® membranes with varying levels of hydration can produce dramatic changes in mechanical properties. For this reason, a selection of samples is further processed by HIP at pressures of 45,000psi and temperatures in the range of 100 ? 200°C.

Composite membranes are created by adding ceramic to the milling step of the preparation. The effect of adding up to 20 wt% ceramic on the thermal and mechanical properties of the material will be discussed. The influence of ceramic content on hydration will also be determined. Additionally, an effort will be made to determine the distribution of the inorganic phase within the membranes.

[1] R.B. Moore, K.M. Cable, and T.L. Croley, Barriers to flow in semicrystalline ionomers. A procedure for preparing melt-processed perfluorosulfonate ionomer films and membranes, J. Membr. Sci., 75 (1992) 7-14