Lifetime and Performance Prediction of SOFC Anodes Operated with Trace Amounts of Hydrogen Sulfide

Abstract

An elementary kinetic model is developed to predict the influence of sulfur on Ni/YSZ anodes of solid oxide fuel cells (SOFC) performance. A multi-step reaction mechanism describing the formation and oxidation of sulfur on the Ni surface is coupled with gas transport in the channel and porous phase, and charge-transfer processes. A thermodynamic and kinetic data set of sulfur formation and oxidation is derived based upon various literature sources including a coverage-dependent description of the enthalpy of surface-adsorbed sulfur. The validity of the model is demonstrated on two SOFC operation modes, namely H2/H2O/H2S and CH4/H2/H2O/H2S fuel mixtures, at different operating conditions using various electrochemical literature experiments. The first concern is the influence of adsorbed sulfur on charge-transfer processes and the second concern is the effect of adsorbed sulfur on complex methane reforming chemistry. The results reveal that sulfur surface coverage increases with current density demonstrating a low sulfur oxidation rate.