Transient multiscale modeling of aging mechanisms in a PEFC cathode

In this paper we propose a mechanistic model of the electrochemical processes in a polymer electrolyte fuel cell cathode, focusing on aging phenomena. The proposed model is based on a nonequilibrium thermodynamics approach previously developed by us, describing the transient response to current perturbations of an electrochemical double layer at the catalyst/Nafion-electrolyte interface. It describes the internal dynamics of the electrochemical double layer, taking into account the coupling between the transport of protons and Pt2+ in the diffuse layer, as well as the carbon-supported Pt coarsening, the Pt oxidation, the oxygen reduction reaction, and the water dipoles adsorption in the inner layer. This continuous nanoscale interfacial model is coupled with a microscale model of the oxygen transport through the impregnated Nafion layer and is designed to be coupled with a continuous microscale model of electron, proton, and Pt2+ transports through the membrane-cathode assembly thickness. The model allows analysis of cathodic potential sensitivity to the operating conditions, the initial Pt loading, and to the temporal evolution of the electrochemical activity from aging mechanisms. In particular, the influence of simulated time on the impedance spectra pattern is studied. (C) 2007 The Electrochemical Society.