Modeling Ion Transport in Fuel Cell Electrodes including Water|Electrolyte Interfaces and Electric Double Layers

Abstract

We present a computational model for studying ionic transport within water-filled pores inside polymer electrolyte fuel cell (PEFC) catalyst layers. The model features the interface between a water-filled pore and polymer electrolyte, and the electric double layers (EDLs) that form at the water|polymer electrolyte interface and at the charged walls of the pores. This model is applicable to several catalyst layer scenarios, including ionic transport within ionomer-free nanostructured thin-film (NSTF) electrodes, ionomer-free pores within catalyst particle agglomerates, and the micropores within catalyst support particles. We investigate the coupling of the distributed electrochemical reactions and the EDL physics, and their effect on the overall catalyst layer performance through both the kinetics and transport. An important finding is the significant impact that the polyelectrolyte film's Donnan potential has on the reaction distribution along the pore.