Fuel Cell Membranes

Servet Nadirler, Sanjeev Mukerjee, and Al Sacco, Jr.

Fuel cells are promising energy sources as alternatives to internal combustion engines, since they offer cleaner and more efficient energy production. Polymer Electrolyte Membrane (PEM) Fuel Cells have various advantages compared to other types. They have low weight, and volume. They only need hydrogen, oxygen and water to operate and do not require corrosive fluids. Their operating temperatures are relatively low (?80-120 oC); this feature allows them to start up quickly. Also, it results in less wear on the components, allowing a longer lifetime. The cell does not produce any green house gases, thus it is a clean energy source. These advantages differentiate PEM fuel cells form the other types, and make them a promising candidate for transportation applications.

PEM fuel cells utilize a polymeric membrane to transfer hydronium ions from anode to cathode. Perfluorinated polymeric membranes are currently used in PEM fuel cells. These membranes are good proton conductors in the presence of water. However, conductivity level decreases above 100 oC due to the fast evaporation rate of water. They also have low glass transition temperatures causing chemical degradation. Their high cost prevents the commercial use of PEM fuel cells. To improve the physical properties of polymeric membranes (e.g., ionic conductivity and water retention at high temperatures and low relative humidity levels), manufacture of hydrocarbon polymeric membranes with higher glass transition temperatures and fabrication of composite membranes that incorporate inorganic fillers are pursued.

This research focuses primarily on investigating ionic conductivity of composite membranes. Several types of zeolites are incorporated in both perfluorinated and hydrocarbon polymeric matrices. Conductivity measurements are performed at relative humidity levels ranging from 40 to 100% and temperatures ranging from room temperature to 100 oC. Other physical properties, such as water uptake levels and ion exchange capacities, are also determined to better understand conductivity measurements. Results are compared with Nafion 117, the most efficient perfluorinated polymeric membrane on the market. Preliminary results show that polymeric membranes that incorporate protonated type zeolites with high silicon to aluminum ratio improve the conductivity of the pure polymeric matrices. This improvement is more significant at 80% relative humidity levels and 100 oC.