Spatially-Resolved Modeling of Electric Double Layers for the Oxygen Reduction Reaction in Water-Filled Platinum Electrodes

Abstract

We present a computational model for studying ion transport and reaction kinetics within water-filled pores of an ionomer-free, thin film Pt cathode inside polymer electrolyte fuel cell (PEFC). The model resolves the electric double layers (EDLs) at the water|Pt and water|membrane interfaces. We investigate the coupling of the distributed electrochemical reactions and the EDL physics, and their effect on the overall electrode performance through both the kinetics and transport. Oxygen reduction reaction (ORR) is resolved locally along the pore wall, where both acidic and alkaline mechanisms are included due to a large axial variation in pH along the pore. An important finding is the significant contribution of the alkaline mechanism to the overall current at high applied potentials and its contribution to the ionic conductivity within the water-filled pore.