Investigating Oxygen Reduction Reaction Using a Multiscale Modeling Approach for Polymer Electrolyte Membrane Fuel Cell

Abstract

Cathode catalyst layer (CCL) modeling is an important tool in elucidating the coupled transport-reaction phenomena and optimizing electrode architectures for greater efficiency, power density, and durability and thereby, reducing fuel cell costs. State-of-the-art catalyst use a high surface area carbon black (HSC) that supports platinum (Pt) nanoparticles, where some of the Pt particles reside on the carbon surface and a significant fraction of particles are found in the nm-scale pores of the carbon support. Within the electrode, the catalyst in bound by a polymer electrode binder (i.e., ionomer) that coats the external surface of the catalyst but does not penetrate the internal pores that are filled with liquid water due to capillary condensation. The contact of ionomer with Pt is known to reduce electrocatalytic activity due to site-blocking by the ionomer anion as well as increase the oxygen transport resistance. There is very little prior work on modeling the distinct performance of the internal Pt and the external Pt in contact with the ionomer. Most prior attempts to model CCLs with HSC catalyst supports at the MEA-scale and cell-scale have used an uncoupled approach, that separately considered the transport to the internal and external Pt particles, not considering the combined flux of oxygen through the ionomer film. Thus, the prior uncoupled model could potentially underestimate the oxygen concentration drop through the ionomer film. Here, we have adopted a numerical model of the catalyst that simultaneously considers the transport to the internal and external Pt as well as the different transport properties in the water and ionomer domains in single primary particle of the catalyst. The single spherical catalyst support model is upscaled to a 3D fuel cell model using a parametric linear regression fitting to model the local source/sink terms in the CCL. This multi-scale model is then applied to study the impact of the catalyst morphology.This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office, Award Number DE-EE0008822.