$Ce0.8M0.2O2−δ$$(M=Mn,Fe,Ni,Cu)$ as SOFC Anodes for Electrochemical Oxidation of Hydrogen and Methane

Oxide anodes such as doped ceria offer improved tolerance for nonidealities in anode environment such as redox cycles, sulfur and other poisons, and hydrocarbons. Mixed-valence transition element in ceria provides an additional redox couple besides $Ce4+∕Ce3+$ in reduced atmosphere, facilitating its electrocatalytic reaction for oxidation of fuels. This paper presents the electrochemical characteristics of $Ce0.8M0.2O2−δ$$(M=Mn,Fe,Ni,Cu)$ for oxidation of hydrogen and methane. $Ce0.8M0.2O2−δ$ was synthesized, and crystal phase analysis by X-ray diffraction was performed. Single-phase $Ce0.8M0.2O2−δ$$(M=Mn,Fe,Ni)$ were formed. A second phase, CuO, was found in the powders with the nominal composition of $Ce0.8Cu0.2O2−δ$⁠. $Ce0.8M0.2O2−δ$ exhibited stability in reducing atmosphere. In comparison, similar microstructural characteristics were found for $Ce0.8M0.2O2−δ$$(M=Mn,Fe,Cu)$⁠. However, $Ce0.8Ni0.2O2−δ$ exhibits poor microstructure with large cracks. The electrochemical oxidation of wet hydrogen and wet methane was investigated with impedance spectroscopy by using the three-electrode configuration. It was found that $Ce0.8M0.2O2−δ$$(M=Mn,Fe,Ni,Cu)$ demonstrates relatively low electrochemical activity in both hydrogen and methane. Regarding low $n$-type conductivity of transition metal cation-containing ceria, it was suggested that an oxide with a high electronic conductivity be added into the $Ce0.8M0.2O2−δ$ matrix for improvement of the electrode performance.