Kinetics of Carbon Monoxide Electro-Oxidation in Solid-Oxide Fuel Cells from Ni-YSZ Patterned-Anode Measurements

A mathematical model is developed around the framework of a reduced mechanism describing electrochemical oxidation of carbon monoxide on Ni-YSZ patterned anodes. The electro-oxidation mechanism involves three reactions, one describing adsorption/ desorption of COonNi, and two single-electron charge-transfer steps inwhich the surface adsorbate CO(Ni) participates directly. These steps are coupled with surface transport in a reaction-diffusion model for which analytic equilibrium and steady-state solutions are derived. As much as possible, we make use of existing, independent, published information about heterogeneous chemistry, surface transport, and other model parameters. The only unknowns in our model are taken to be the kinetic rate constants of the electrochemical reactions, which we evaluate by fitting the model predictions to previously published patterned-anode experiments [B. Habibzadeh, Ph.D. Thesis, University of Maryland, College Park, MD, USA (2007)]. The results show that diffusion of CO on the Ni surface to the three-phase boundary is the rate-controlling process for CO electro-oxidation. Moreover, from a reaction standpoint, the charge-transfer process is dominated by a slow step involving CO(Ni). These findings collectively demonstrate the critical dependence of the electro-oxidation process to the direct participation of CO. © 2013 The Electrochemical Society. All rights reserved.