Electrocatalytic Activity Analysis of PEFC Cathode by 1-D Macrohomogeneous Model of Catalyst Layer

Abstract

A simple macrohomogeneous 1-D model of the polymer electrolyte fuel cell (PEFC) cathode catalyst layer incorporating ORR kinetics and including the effects of Pt surface oxide coverage, proton migration, and oxygen diffusion is introduced. In the model, both the site-blocking and the energetic effects of the Pt surface oxide are incorporated and applied to actual fuel cell data. Measured polarization curves are fitted in both the cathodic and anodic directions using a single value of the intrinsic exchange current density (that is independent of the Pt oxide coverage) representing the entire potential range of operation. By fitting with this model, the catalytic activity is broken down into the intrinsic exchange current density, the oxide coverage, and the Temkin parameter. The fitting parameters used in the model are the exchange current density, the Temkin parameter, and the transmissibility of oxygen within catalyst layer. The electrochemically active surface area and the proton conduction resistance within catalyst layer were determined using experimental diagnostic techniques. The surface charge representing oxide species was also measured experimentally and converted into a surface coverage based on an assumed species. The analysis of polarization curves using this modeling approach may help to provide a deeper understanding that could accelerates the development and characterization of new catalysts.