pp

The study of oxygen transport in PEM fuel cells requires consideration of water transport as well. Because water can appear in both vapor and liquid form, heat transport must also be considered. The flow-field channels, the diffusion medium, the micro-porous layer, and the electrode all influence transport in different ways, and it is desirable to be able to understand transport limitations in each of these components separately. We will explain how oxygen transport limiting current can be used to study transport in all of these components and briefly outline a model of oxygen, water, and heat transport that arose from the study of limiting current. Fig. 1 shows polarization curves taken with a 5cm2 differential cell, using different dilute concentrations of oxygen in nitrogen for the cathode gas feed. At each concentration of oxygen, the polarization curve reaches a limiting current at which the curve becomes vertical. (The current increases occurring below 0.1 V are due to hydrogen evolution and can be ignored in the determination of limiting currents.) The cell oxygen transport resistance OR is given b