4.2: Modeling of Proton Exchange Membrane Fuel Cells
4.2 Modeling of Proton Exchange Membrane Fuel Cells
In a PEMFC, the electrolyte is a perfluorosulfonic acid membrane with higher proton conductivity than any conventionally strong acid ( e.g., H 2 SO 4, HCl, and HClO 4). The backbone structure of the membrane polymer is the polytetrafluoroethylene (PTFE), also known as the strongly hydrophobic Teflon. Side chains ending with the sulphonic acid ( HSO 3) are tethered to the backbone polymer, forming the Nafion type membrane materials. Since the HSO 3 group is ionically bonded, the side chains tend to cluster within the overall structure through the strong attraction between the H + and SO ? 3 ions. The sulphonic acid is highly hydrophyllic; consequently, the Nafion materials consist of a generally hydrophobic bulk with hydrophyllic regions ( i.e. sulphonic sites). With adequate adsorption of water molecules, acid solution forms within the sulphonic sites, and protons may be conducted through the network of hydrated regions. The catalyst layer is a porous mixture of the electrocatalyst and the proton-conducting membrane, where fine particles of platinum are dispersed on carbon supports to maximize the reaction area. Porous carbon cloth or paper are the materials for the electrodes, which may further contain Teflon to prevent water flooding. The bipolar plates in the cell stack are usually made of graphite, while stainless steel or titanium may also be used.
Several technical challenges for the application of PEM fuel cells include (i) managing water and...