Abstract
Ceria is being considered as an electrocatalyst component for fuel-flexible SOFC anodes. With Ce3+ and Ce4+ oxidation states, ceria can function as a mixed ionic-electronic conductor, transporting both O2- ions and electrons. It remains unclear what role these oxidation states play during SOFC operation. This study addresses these issues using ambient-pressure XPS in a single-chamber cell to characterize thin-film CeO2-x electrodes on a YSZ electrolyte during electrochemical oxidation of H2 and reduction of H2O at 620 {degree sign}C. Voltage-current curves for the ceria film electrodes reveal sharp changes in resistance as a function of applied voltage from positive to negative bias. XPS measurements during electrochemical characterization show the extent of near-surface Ce4+ reduction to Ce3+ with increasing cell voltage. Increased oxidation to Ce4+ at large negative voltages correlates with a resistance drop due to H2 oxidation activity. These findings provide insight into how CeO2-x influences electrochemical fuel oxidation or H2O reduction.
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