278727 Spatially-Resolved Modeling of Oxygen Reduction Reaction Inside Polymer Electrolyte Fuel Cell Cathode's Water-Filled Mesopore

Wednesday, October 31, 2012: 2:29 PM
322 (Convention Center )
Iryna V. Zenyuk and Shawn E. Litster, Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA

In this work we study the effects of water-filled mesopores on the oxygen reduction reaction (ORR) in the cathode catalyst layer of a polymer electrolyte fuel cell. We model reactions in water-filled pores with a multi-scale, multi-dimensional numerical framework, where oxygen and proton transport, kinetics and surface chemistry are spatially resolved. Poisson-Nernst-Planck theory describes charge transport and potential distributions in the water-filled pore, adjacent Nafion polymer electrolyte film and carbon wall. The model incorporates spatially resolved, coupled electric double layers (EDLs) at water|Nafion and water|electrode interfaces. We also use the Stern modification for the Guoy-Chapman EDL theory to account for dielectric saturation and ion specific adsorption at the inner Helmholtz plane (IHP), which is modeled as a finite-thickness domain. The carbon wall domain includes a surface complexation model to account for carbon black catalyst support’s surface chemistry and a space-charge layer to account for the electron spillover effect. The ORR is modeled with multi-step, double-trap model where the driving potential is the difference between the potential at the wall and that at the outer Helmholtz plane. Our results show that water-filled pore is kinetically limited due to proton depletion at high interfacial potentials. The pore surface area next to the Nafion electrolyte produces the most current, whereas the rest of the pore contributes very little to the overall ORR reaction. We also compare the results of water-filled pore to Nafion-filled pore and present the values for ORR effectiveness factor.

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See more of this Session: Fuel Cell Technology
See more of this Group/Topical: Fuels and Petrochemicals Division