Operando optical studies of sulfur contamination in syngas operation of solid oxide fuel cells

Abstract

Near-infrared thermal imaging, voltammetry, and chronocoulometry have been used to examine electrochemical oxidation mechanisms in solid oxide fuel cells (SOFCs) operating with model syngas mixtures (CO + H2) at 800 °C with and without a sulfur-containing contaminant. Questions persist regarding the electrochemical oxidation of H2 vs. CO especially on the role of CO activation and CO mobility in porous SOFC cermet anodes. Chronocoulometry, electrochemical impedance spectroscopy, and operando optical methods are also used to characterize contaminant effects of SOFC operation at 800 °C in the presence of 50 ppmv sulfur to gain insight into its effect on syngas SOFC operation. The chronocoulometry results indicate that in the absence of sulfur contaminants, electrochemical oxidation of adsorbed CO does not contribute to current production, possibly because of rapid carbon formation at the anode surface. This discovery suggests that initially adsorbed H2 is the primary source of charge at early times in the electro-oxidation of syngas fuels. Furthermore, in the presence of sulfur contaminants, chronocoulometry data show that S competitively occupies ~30% of the electroactive sites at the triple phase boundary and contributes to the total initial charge likely via electrochemical oxidation of S to SO2.