Modulating Lattice Oxygen Activity of Iron-Based Triple-Conducting Nanoheterostructure Air Electrode via Sc-Substitution Strategy for Protonic Ceramic Cells

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 BaFe0.6Ce0.2Sc0.2O3-delta (BFCS) perovskite is rationally designed by a facile Sc-substitution strategy for BaFe0.6Ce0.4O3-delta (BFC) as efficient and stable air electrode for PCCs. The BFCS electrode with an optimized Fe 3d-eg orbital occupancy and more oxygen vacancies exhibits a polarization resistance of approximate to 0.175 omega cm2 at 600 degrees C, approximate to 1/3 of the BFC electrode (approximate to 0.64 omega 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+-O2- 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 degrees C. These results highlight the importance of activating lattice oxygen in air electrodes of PCCs. The BFCS air electrode formed by Sc-substitution has significantly enhanced lattice oxygen mobility, creating abundant oxygen vacancies and active sites, which contribute to the adsorption and dissociation of oxygen species, mass transfer, and charge transfer electrochemical processes in electrode reactions (ORR/OER). image