Multiscale model of carbon corrosion in a PEFC: Coupling with electrocatalysis and impact on performance degradation

In this paper we propose a mechanistic model describing the coupling between the polymer electrolyte fuel cell (PEFC) membrane electrodes assembly (MEA) electrocatalysis and the cathode carbon catalyst-support corrosion. The electrocatalysis description includes our previously introduced irreversible thermodynamics nanoscale models of the electrochemical reactions (hydrogen oxidation reaction/oxygen reduction reaction) coupled with the catalyst/ionomer interface double layer phenomena. Physically, the model describes the feedback between the instantaneous performance and the intrinsic cathode carbon oxidation process. It allows exploring the impact of the operating conditions (nominal current, reactant gas pressures, temperature, etc.) and the initial electrodes compositions (carbon and platinum loadings) on the PEFC MEA durability. Some numerical simulations show agreement with experimental knowledge already reported in literature, in particular, when the anode chamber is partially exposed to oxygen (induced by polymer electrolyte membrane crossover or fuel starvation), cathode thickness decrease and cell potential decay are predicted. Furthermore, we found that cathode damage increases as platinum loading increases and as platinum nanoparticles size decreases. Moreover, carbon corrosion favors the platinum coarsening; competition between carbon oxidation reaction and electrocatalytic mechanisms is investigated. Simulations also suggest that an "optimal" external load current inducing a "maximal" durability exists. The sensitivities of the electrochemical impedance spectra to the operating conditions and simulated operation time are also provided. (c) 2008 The Electrochemical Society.