Effect of a Rigid Gas Diffusion Media Applied as Distributor of Reagents in a PEMFC in Operation, Part II: Wet Gases.

Several mass transport phenomena occur during the operation of a PEMFC each one generates a resistance implying limitations during operation. The humidity in the reactive gas flows promotes the conductivity of the electrolyte membrane but increases the transport limitations at high current densities. The reactive gases are distributed in a conventional PEMFC by distributors with serpentine-shaped channel, transversely covering the surface of the electrodes. This paper applies and compares a rigid gas diffusion media as gas distributor, its porosity comprises mostly of macropores, their function is improve the gases reaction distribution with the aim of reducing resistance to mass transport, in turn collects (in the anode) or distributes (on the cathode) electrons generated in the reaction sites. The results determine a complex mass transport processes in the porous media when the reagents are moistened, however at pressures greater than 10 psig, the functionality of the PEMFC is increased significantly to moisture conditions in the reagents flow and it is very favorable for the case of conventional PEMFC design. The combined effect Pressure- Humidity reduces ohmic limitations to medium current densities, while the flow rate allows a reduction in transport resistance at high current densities. The presence of heavy metals in the structure of the commercial electrodes may generate over-potentials in the cell with capacity to affect the functionality of PEMFC.