The Role of Surface Carbon in Oxidation of Ethylene and Toluene on Platinum-Ceria Anodes for Solid Oxide Fuel Cells

Abstract

Surface reactions of ethylene and toluene on a Pt-modified, samarium-doped ceria (Pt/CSO) anode were examined as a function of hydrocarbon to oxygen ratio and cycling of oxy- gen ion current through the electrolyte. Reaction conditions were temperatures of 540 °C (C2H4) and 730 °C (C7H8), hydro- carbon partial pressures of 0.001-0.04 Torr, and oxygen partial pressures of 0.1 Torr (anode) and 5 Torr (cathode). A gen- eral result is that reactions of both ethylene and toluene are strongly sensitive to surface carbon. A step change in oxygen ion current results in electrochemical enhancements of up to 80 and catalytic enhancements as high as 3. Cycling of oxygen ion currents leads to enhanced catalytic activity that remained for 1 hour or more after cycling was terminated. Enhance- ment was sensitive to the ratio of hydrocarbon to oxygen and attributed to a combination of carbon removal and redox ki- netics in the ceria anode.