Modulating Lattice Oxygen Activity of Iron-Based Triple-Conducting Nanoheterostructure Air Electrode via...

Iron-based perovskite air electrodes for protonic ceramic cells (PCCs) offer broad application prospects owing to their reasonable thermomechanical compatibility and steam tolerance. However, their insufficient electrocatalytic activity has considerably limited further development. Herein, oxygen-vacancy-rich BaFe_0.6Ce_0.2Sc_0.2O_3-δ (BFCS) perovskite is rationally designed by a facile Sc-substitution strategy for BaFe_0.6Ce_0.4O_3-δ (BFC) as efficient and stable air electrode for PCCs. The BFCS electrode with an optimized Fe 3d-e_g orbital occupancy and more oxygen vacancies exhibits a polarization resistance of ≈ 0.175 Ω cm² at 600 °C, ≈ 1/3 of the BFC electrode (≈0.64 Ω cm²). Simultaneously, BFCS shows favorable proton uptake with a low proton defect formation enthalpy (- 81 kJ mol^-1). By combining soft X-ray absorption spectroscopy and electrical conductivity relaxation studies, it is revealed that the enhancement of Fe⁴⁺-O^2- interactions in BFCS promotes the activation and mobility of lattice oxygen, triggering the activity of BFCS in both oxygen reduction and evolution reactions (ORR/OER). The single cell achieves encouraging output performance in both fuel cell (1.55 W cm^-2) and electrolysis cell (-2.96 A cm^-2 at 1.3 V) modes at 700 °C. These results highlight the importance of activating lattice oxygen in air electrodes of PCCs.