Development of a Casting Technique for Membrane Material Used in High-Temperature PEM Fuel Cells

This paper describes research work associated with development of a casting test bed for a polyphosphoric acid (PPA) based membrane material used in high-temperature PEM fuel cells with operating temperatures up to 160°C. Casting of this material is difficult due to its high viscosity, temperature-dependent rheological properties, curing tendencies, and corrosiveness at high temperatures. To design appropriate casting equipment, important physical and mechanical properties of this new membrane material have been characterized. Specifically, the rheological behavior of the solution at different concentrations of PPA was determined for use in casting system design. Based on these properties, various casting techniques other than the standard doctor blade film application used for laboratory work were investigated, including stencil printing on a substrate, stencil printing directly on a gas diffusion electrode, nip roller extrusion, and slot die extrusion. As a result, a manufacturing test bed that allows for temperature and humidity control during casting was designed and fabricated to conduct various experiments. Subsequent experiments show that slot die extrusion is the most promising casting method to cost effectively, continuously, and uniformly cast the membrane material.