Nanocomposites: A New Opportunity for Developing Highly Active and Durable Bifunctional Air Electrodes for Reversible Protonic Ceramic Cells

Reversible protonic ceramic cells (RePCCs) can facilitate the global transition to renewable energy sources by providing high efficiency, scalable, and fuel‐flexible energy generation and storage at the grid level. However, RePCC technology is limited by the lack of durable air electrode materials with high activity toward the oxygen reduction/evolution reaction and water formation/water‐splitting reaction. Herein, a novel nanocomposites concept for developing bifunctional RePCC electrodes with exceptional performance is reported. By harnessing the unique functionalities of nanoscale particles, nanocomposites can produce electrodes that simultaneously optimize reaction activity in both fuel cell/electrolysis operations. In this work, a nanocomposite electrode composed of tetragonal and Ruddlesden–Popper (RP) perovskite phases with a surface enriched by CeO2 and NiO nanoparticles is synthesized. Experiments and calculations identify that the RP phase promotes hydration and proton transfer, while NiO and CeO2 nanoparticles facilitate O2 surface exchange and O2‐ transfer from the surface to the major perovskite. This composite also ensures fast (H+/O2‐/e‐) triple‐conduction, thereby promoting oxygen reduction/evolution reaction activities. The as‐fabricated RePCC achieves an excellent peak power density of 531 mW cm‐2 and an electrolysis current of −364 mA cm‐2 at 1.3 V at 600 °C, while demonstrating exceptional reversible operation stability of 120 h at 550 °C. A nanocomposite concept is proposed to develop an excellent air electrode for reversible protonic ceramic cells (RePCCs). Sr0.9Ce0.1Fe0.8Ni0.2O3‐δ (SCFN) is a highly promising nanocomposite air electrode material for RePCCs, possessing high activity toward the oxygen reduction/evolution reaction and water formation/water‐splitting reaction. SCFN is suitable for the sustainable and stable operation of fuel cells and in electrolysis mode.