Facile anion engineering: A pathway to realizing enhanced triple conductivity in oxygen electrodes for reversible protonic ceramic electrochemical cells

Reversible proton ceramic electrochemical cells (R-PCECs) have emerged as a promising solution for sustainable energy conversion and storage at intermediate temperatures. However, the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics at the air electrodes of R-PCECs limit the cell performance. To achieve improved ORR/OER catalytic performance, we propose a practical approach of strategic anion engineering on the oxygen site of air electrode materials. Specifically, the popular triple H⁺/e⁻/O²⁻ conducting oxide (TCO) Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) is selected to enhance the limiting H⁺/O²⁻ generation and migration processes as an efficient air electrode for R-PCECs. By introducing different electronegative elements (F and Cl) to weaken metal-oxygen bonds (M-O), the oxygen chemical environment of the electrode material was optimized, thereby promoting surface oxygen exchange and O²⁻/H⁺ bulk migration. The resulting Ba_0.5Sr_0.5Co_0.8Fe_0.2O_2.9-σF_0.1 electrode exhibits enhanced proton uptake/mobility and catalytic activity for ORR and OER, as well as improved stability. This research offers a rational design strategy for engineering high-performance R-PCEC air electrodes with enhanced operating stability for efficient and sustainable energy conversion and storage.