Proton exchange membrane fuel cell contamination model: Competitive adsorption followed by a surface segregated electrochemical reaction leading to an irreversibly adsorbed product

A generic, transient fuel cell kinetic loss mathematical model was developed for the case of contaminants that partially cover the catalyst surface with irreversibly adsorbed products. The model was derived using step changes in contaminant concentration, constant operating conditions and disregarding liquid water scavenging effects. The closed form solutions were validated using H2S, SO2 and COS data from a single source. The model needs to be validated against other data sets and transient operating conditions more representative of automotive applications. A method is proposed to determine kinetic rate constants and relies on tests with a reactant, a contaminant and, a reactant and a contaminant mixture. The method is useful to evaluate the presence of interactions between reactant and contaminant related adsorbates, and, to minimize electrode potential variations during controlled cell voltage measurements. Model parameters were similar for all contaminants suggesting a common adsorbate configuration. The model also expands the number of previously derived cases. All models in this inventory, derived with the assumption that the reactant is absent, lead to different dimensionless current vs. time behaviors similar to a fingerprint. These model characteristics facilitate contaminant mechanism identification. Model predictions include a limit of 0.7 ppb contaminant concentration in the reactant stream to minimize cell performance losses during the 5000 h automotive application life. This tolerance limit represents a worse case scenario because it does not take into account performance recovery resulting from drive cycle operation or the addition of mitigation strategies. A cell performance loss increase of 40% is also predicted for a catalyst loading decrease from 0.4 to 0.1 mg Pt cm(-2). (C) 2010 Elsevier B.V. All rights reserved.