Proton Exchange Membrane Fuel Cells: Development of Novel Materials for Use as Proton Exchange Membranes

Principal Investigator: Joseph M. DeSimone
Departments of Chemistry and Pharmacology

In the DeSimone Group at UNC-Chapel Hill, research is being conducted to realize the potential of alternative fuels such as hydrogen or methanol through the use of proton exchange membrane fuel cells (PEMFCs). PEMFCs are considered the front-runners for the use of alternative fuels for transportation purposes.

At the heart of the PEMFC is the proton exchange membrane (PEM). The PEM (sometimes referred to as the electrolyte) is sandwiched in between two electrodes to form a Membrane Electrode Assembly (MEA). The two electrodes, the anode and the cathode, are where the fuel (hydrogen or methanol) and the oxidant (oxygen or air) respectively, are consumed to create electrical energy. The membrane plays three crucial roles: (1) it serves as a mechanical separator between the anode and cathode, (2) allows protons generated at the anode to migrate to the cathode (referred to as conduction), and (3) prevents crossover, or the migration of the reactants to the opposite electrode. When hydrogen is used as the fuel, the only byproduct is benign water, which is in stark contrast to the environmentally unfriendly byproducts produced by internal combustion engines.

A Schematic of a PEMFC

Nafion, the current gold standard PEM material, is expensive and does not work well in low humidity environments. The PEMs developed at UNC are better proton conductors than Nafion (see below), which is remarkable considering how many state of the art PEMs struggle just to match Nafion's proton conductivity. Another unique feature of the PEMs developed at UNC is their topology. UNC's materials are crosslinked, which means the polymers chains that compose the membrane interconnect and form a network. Unlike linear PEMs like Nafion, the crosslinked UNC materials will not dissolve in water as the number of conducting sites increases. PEMs with more conduction sites (referred to as having a higher IEC) are able to absorb water better, thus diminishing the reliance on humidity for transportation of water. Materials developed at UNC could thus be synthesized with a variety of different conductivities.