Experiencing heightened oxygen reduction response in CaFe₂O₄-WO₃ heterostructure for ceramic fuel cells

A fundamental understanding of oxygen reduction reaction (ORR) is essential for low-temperature solid oxide fuel cells (LT-SOFCs). In this work, following our previous studies of protonic ceramic fuel cell (PCFCs) cathode material, CaFe₂O₄-WO₃ heterostructure composite material is used as an air electrode over oxide ion conducting electrolyte ceramic fuel cell. CaFe₂O₄-WO₃ as a cathode over Sm-doped CeO₂ (SDC) electrolyte exhibits a very low area-specific resistance (ASR) of 0.18 Ω cm² and excellent power output of 842 mW-cm⁻² at 500 °C. The CaFe₂O₄-WO₃ cathode showed improved electrochemical performance in LT-SOFC compared to PCFCs [1]. The excellent ORR activity of CaFe₂O₄-WO₃ could mainly be assisted with the superficial release of oxygen ions than the protons with enhanced incorporation abilities through the interface of CaFe₂O₄-WO₃ heterostructure. Moreover, engineering the heterostructure by forming complex oxidation states at the interface of CaFe₂O₄-WO₃ narrows the band gap. It can effectively facilitate small polaron hopping of valence electrons and diffusion of oxygen ions, resulting in high electrical conductivity and electrocatalyst function in SOFCs. In addition, various spectroscopic and density functional calculations are employed to catch the understanding of CaFe₂O₄-WO₃ heterostructure composite as a new functional ORR electrocatalysts for advanced LT-SOFCs.