Gas diffusion media, flowfields and system aspects in low temperature fuel cells

Abstract: Most of the transport processes of a fuel cell take place in the gas diffusion media and flow fields. The task of the flow field is to uniformly distribute the reactant gases across the electrochemically active area and at the same time ensure an adequate removal of the reactant products, which is water on the cathode side in both polymer electrolyte membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC). Gas diffusion media are required to supply the reactant under the land areas of the flow field; at the same time, the gas diffusion media has to ensure a good thermal as well as water management to avoid any non-optimum conditions. Characterization tools for gas diffusion media are presented, flow field types and design criteria are discussed and the effect of both components on the performance of a fuel cell are highlighted. System aspects for different fuels (hydrogen, vapor-fed DMFCS, liquid fed DMFCs) are compiled and the different loss contributions and factors determining the performance of a fuel cell system are shown.