Redox-Reversible Electrode Material for Direct Hydrocarbon Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) can directly operate on hydrocarbon fuels such as natural gas; however, the widely used nickel-based anodes face grand challenges such as coking, sulfur poisoning, and redox instability. We report a novel double perovskite oxide Sr₂Co_0.4Fe_1.2Mo_0.4O_6-δ (SCFM) that possesses excellent redox reversibility and can be used as both the cathode and the anode. When heat-treated at 900 °C in a reducing environment, double perovskite phase SCFM transforms into a composite of the Ruddlesden-Popper structured oxide Sr₃Co_0.1Fe_1.3Mo_0.6O_7-δ (RP-SCFM) with the Co-Fe alloy nanoparticles homogeneously distributed on the surface of RP-SCFM. At 900 °C in an oxidizing atmosphere, the composite transforms back into the double perovskite phase SCFM. The excellent oxygen reduction reaction catalytic activity and mixed ionic-electronic conductivity make SCFM an excellent cathode material for SOFCs. When SCFM is used as the anode, excellent performance and stability are achieved upon either direct oxidation of methane as a fuel or operation with sulfur-containing fuels. The excellent redox reversibility coupled with outstanding electrical and catalytic properties manifested by SCFM will enable a broad application in energy conversion applications.