Electrochemical Carbon Removal Mechanisms in Solid Oxide Fuel Cells: An Optical and Electrochemical <i>Operando</i> Study

This study employed complementary optical and electrochemical methods to identify mechanisms responsible for the electrochemical removal of carbon from commercial Ni-yttria stabilized zirconia (YSZ) cermet anodes in functioning solid oxide fuel cells (SOFCs) operating at 800 °C. Near infrared thermal imaging (NIRTI), Fourier-transform infrared emission spectroscopy (FTIRES), and chronoamperometry (CA) were used to measure changes under an inert atmosphere to a carbon-contaminated anode after an overpotential is applied. NIRTI showed that the thermal processes accompanying the electrochemical oxidation of carbon is symmetrical around the current collector when the device is operated under potentiostatic conditions. FTIRES showed a steep rise of both CO and CO 2 produced and similarly steep fall in the amount of CO while the concentration of gas phase CO 2 remains relatively constant as the carbon is oxidized. The evolution of the chronoamperometry data together with the NIRTI and FTIRES data show that carbon oxidation is heterogeneous with carbon closest to the current collector being removed at higher currents and carbon further away being electrochemically oxidized at lower currents. These observations suggest electrochemical carbon oxidation processes dominate at higher currents and catalytic carbon gasification by the electrochemical products dominate at lower currents.