Large oxygen reduction response of CaFe2O4-WO3 heterostructure composite for protonic ceramic fuel cell cathode

Protonic Ceramic fuel cells (PCFCs) hold great promise for many applications; however, their high operating temperature hinders their commercial use in practice. The crucial issue that limits the electrochemical performance of PCFCs (including oxygen and proton-ion-conducting) is the sluggish oxygen redox reaction (ORR) at the cathode surface at low operating temperatures. Herein, we have developed a CaFe2O4-WO3 heterostructure composite by interface-vacancy engineered for an efficient ORR electrocatalyst for LT-PCFCs. The CaFe2O4-WO3 heterostructure composite exhibits very low cathodic area-specific resistance (ASR) and high oxygen reduction reaction (ORR) activity response at low operating temperatures of 400–550 °C using a BaCe0.7Zr0.2Y0.1O3-δ (proton-conducting) electrolyte. We have demonstrated high-power density of 585 ± 2% mW-cm−2 with a current density of 1660 mA-cm−2 at 550 °C with H2 fuel and atmospheric air as oxidant and even with possible operation at 400 °C. Moreover, the CaFe2O4-WO3 heterostructure composite shows a very low proton migration energy and activation energy compared to individual CaFe2O4 and WO3, helping to promote ORR activity. Various spectroscopic measurements, such as X-ray diffraction, high resolution transmission electron microscopy (HR-TEM), U-visible spectroscopy (UV–visible), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations are employed to understand the interfacial properties for the improved ORR electrocatalytic activity of the CaFe2O4-WO3 heterostructure composite cathode. Our obtained experimental and theoretical results can further help to develop functional cobalt-free electrocatalysts for LT-PCFCs.