A Microscopic Continuum Model of a Proton Exchange Membrane Fuel Cell Electrode Catalyst Layer

Abstract

A series of steady-state microscopic continuum models of the cathode catalyst layer (active layer) of a proton exchange membrane fuel cell are developed and presented. This model incorporates O₂ species and ion transport while taking a discrete look at the platinum particles within the active layer. The original 2-dimensional axisymmetric Thin Film and Agglomerate Models of Bultel, Ozil, and Durand [8] were initially implemented, validated, and used to generate various results related to the performance of the active layer with changes in the thermodynamic conditions and geometry. The Agglomerate Model was then further developed, implemented, and validated to include among other things pores, flooding, and both humidified air and humidified O₂. All models were implemented and solved using FEMAP™ and a computational fluid dynamics (CFD) solver, developed by Blue Ridge Numerics Inc. (BRNI) called CFDesign™. The use of these models for the discrete modeling of platinum particles is shown to be beneficial for understanding the behavior of a fuel cell. The addition of gas pores is shown to promote high current densities due to increased species transport throughout the agglomerate. Flooding is considered, and its effect on the cathode active layer is evaluated. The model takes various transport and electrochemical kinetic parameters values from the literature in order to do a parametric study showing the degree to which temperature, pressure, and geometry are crucial to overall performance. This parametric study quantifies among a number of other things the degree to which lower porosities for thick active layers and higher porosities for thin active layers are advantageous to fuel cell performance. Cathode active layer performance is shown not to be solely a function of catalyst surface area but discrete catalyst placement within the agglomerate.