Surface Self‐Assembly Protonation Triggering Triple‐Conductive Heterostructure with Highly Enhanced Oxygen Reduction for Protonic Ceramic Fuel Cells

Abstract Triple‐conducting (H + /O 2− /e − ) cathodes are a vital constituent of practical protonic ceramic fuel cells. However, seeking new candidates has remained a grand challenge on account of the limited material system. Though triple conduction can be achieved by mechanically mixing powders uniformly consisting of oxygen ion–electron and proton conductors, the catalytic activity and durability are still restricted. By leveraging this fact, a highly efficient strategy to construct a triple‐conductive region through surface self‐assembly protonation based on the robust double‐perovskite PrBaCo 1.92 Zr 0.08 O 5+δ , is proposed. In situ exsolution of BaZrO 3 ‐based nanoparticles growing from the host oxide under oxidizing atmosphere by liberating Ba/Zr cations from A/B‐sites readily forms proton transfer channels. The surface reconstructing heterostructures improve the structural stability, reduce the thermal expansion, and accelerate the oxygen reduction catalytic activity of such nanocomposite cathodes. This design route significantly boosts electrochemical performance with maximum peak power densities of 1453 and 992 mW cm −2 at 700 and 650 °C, respectively, 86% higher than the parent PrBaCo 2 O 5+δ cathode, accompanied by a much improved operational durability of 140 h at 600 °C.