(247a) Modeling Porous Electrodes in Fuel Cells and Similar Devices: A Tutorial

As electrochemical technologies become increasingly important in our energy paradigm, there is a need to examine them holistically. For commercialization and optimization, one requires a detailed understanding of the underlying physics and phenomena. Furthermore, for such technologies to become practical, they need to operate at high current densities to minimize various cell costs. This operating space necessitates the need for efficient transport of reactants and removal of products from the reaction site, where it is increasingly recognized how critical this local environment and transport are to performance. Mathematical modeling is ideally suited to understand these various interactions and provide insights and optimization strategies. In this talk, various porous electrodes will be examined in terms of their intrinsic transport phenomena. Technologies to be discussed include proton-exchange-membrane fuel cells (PEMFC), Hydroxide-exchange-membrane fuel cells (HEMFC) and their electrolyzer counterparts.

For PEMFCs, such mass transport is dominated by transport of oxygen molecules to the reaction site within the catalyst layer. For HEMFCs, additional transport limitations including hydroxide ions and perhaps even hydrogen can become important. For electrolysis applications, similar gas-diffusion-electrode (GDE) architectures are being investigated and the various tradeoffs endemic in such structures will be discussed such as reactant water transport. This includes the introduction of the applied-voltage and voltage-loss breakdowns that separate the overall polarization curve into its constitutive parts such that the limiting mechanisms can be ascertained. A key focus of the Tutorial will be in exploring and describing the various transport and competing phenomena within the electrochemical cells and how to describe them physically and numerically.