(522f) Structure and Properties of Polyimide-Poly (ethylene glycol) Films for Fuel Cell Applications
Polymer electrolyte fuel cells have the potential to provide cleaner and more efficient energy. Because of the conduction mechanism for current polymer electrolyte membranes, their performance is limited to relatively low temperatures and high humidity. By using different polymers than have been traditionally used, more versatile operating conditions and better efficiencies may be achieved. Because many different properties are needed for an effective polymer electrolyte membrane, multiple polymers often need to be used. Aromatic polyimides are known to be very stable, both thermally and chemically. Poly (ethylene glycol) has been known to provide proton conduction properties under certain conditions. In the current work, aromatic polyimide and poly (ethylene glycol) (PEG) composite membranes have been synthesized for higher temperature fuel cell polymer electrolyte membrane applications in order to exploit the drastically different properties of the polymers. The polyamic acid precursors were synthesized by a classical one pot poly-condensation method that has been shown to work for many different types of polyamic acids. The poly (ethylene glycol) (Mn 1500) was used in pre-polymerized form and incorporated with the polyamic acids in various ways including both blending and chemical bonding to achieve structural features on a small length scale. These polymer systems were converted to polyimide-PEG systems through thermal imidization. This thermal processing can achieve a variety of film properties easily if varied. The polyamic acid precursors were characterized using Fourier transform infrared spectroscopy. The general structure of the films and their thermal properties were analyzed using thermal gravimetric analysis. Small angle x-ray scattering was used to determine the polymer structure on a length scale between 0.5 and 80 nanometers, because it has been shown that features on this length scale can often lend themselves to achieving good conduction properties. Since acids are often needed to provide any significant conduction properties to polymers, phosphoric acid was incorporated into the films by soaking. The films were then analyzed for protonic conductivity properties using a cyclic voltammetry method. Effects of temperature and stability were studied with regards to the conductivity. These composite systems were analyzed in order to determine composition-structure-property relationships for fuel cell membrane applications as many films are studied for structure or properties but rarely the relationship.