Limiting Current as a Tool to Study Oxygen Transport in PEM Fuel Cells

This survey article reviews the results of three of our papers, which develop limiting current as a tool for studying oxygen transport resistance in PEM fuel cells. Experimental methods are discussed, which allow one to separate the total oxygen transport resistance into its component contributions, as well as to distinguish between resistance due to intermolecular gas diffusion and other diffusion sources, such as Knudsen diffusion or diffusion through liquid water and ionomer. One can also clearly distinguish conditions in which water starts to condense in the cell and measure the impact of this condensation on transport resistance. Special emphasis is given to the question of how to determine when apparent limiting currents are due to transport limitations and when they are caused by other non-related effects. The problem of modeling these processes is also discussed.