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

Abstract

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.