Highly Active Air Electrode with Enhanced Proton Conduction via Isovalent Doping in a Layered Perovskite for Reversible Protonic Ceramic Cells

Reversible protonic ceramic cells (R‐PCCs) offer a compelling solution for efficient energy conversion and storage at intermediate temperatures (400–600 °C); however, their practical implementation and overall electrochemical performance are severely constrained by sluggish electrochemical reaction kinetics at the air electrode. Herein, a novel triple ionic–electronic conducting material is presented, the Ni‐doped layered perovskite PrBa0.5Sr0.5Co1.8Ni0.2O5+δ (PBSCN20), to be utilized as an air electrode in R‐PCCs. Thermogravimetric analysis and density functional theory calculations demonstrate that Ni doping at the Co site significantly promoted oxygen vacancy formation while simultaneously facilitating proton uptake and migration. Consequently, the R‐PCCs with a PBSCN20 air electrode exhibited outstanding electrochemical performance, attaining peak power densities of 1.30 and 0.60 W cm−2 in fuel cell mode, and current densities of −1.72 and −0.41 A cm−2 at 1.3 V in electrolysis mode at 600 and 500 °C, respectively, as well as superior long‐term stability for over 700 h at 500 °C.