Engineering Thermally Resilient and Kinetically Active Reversible Protonic Ceramic Cells via Interfacial Design

Achieving concurrent fast electrode kinetics and long‐term thermo‐mechanical durability remains a critical challenge for reversible protonic ceramic electrochemical cells (R‐PCECs). Herein, we report an interfacial engineering strategy that integrates a perovs.kite‐type PrBaRu 0.1 Co 1.9 O 5+δ (PBRC) nanoparticle layer onto a PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ (PBSCF) substrate (PBRC‐PBSCF), together with a modified pellet‐assisted sintering approach to fabricate dense BaZr 0.4 Ce 0.4 Y 0.1 Yb 0.1 O 3‐δ (BZCYYb4411) electrolytes. The in situ reconstructed heterointerface enhances oxygen reduction/evolution reaction (ORR/OER) kinetics, promotes H 2 O adsorption/dissociation, and improves steam tolerance, as verified by electrochemical measurements and interfacial microstructural analyses. Density functional theory reveals that Ru‐induced electronic modulation at the PBRC‐PBSCF interface lowers the energy of oxygen vacancy formation and optimizes the position of the O 2p band center, thereby accelerating oxygen redox kinetics and stabilizing the interface. The resulting R‐PCECs deliver an excellent peak power density of 1.112 W cm −2 and an electrolysis current density of −1.257 A cm −2 at 1.3 V in 3% H 2 O wet air at 600°C, with a reasonable faradaic efficiency. Furthermore, the cells demonstrate excellent stability, sustaining 100 h of thermal cycling (400–600°C, 200°C h −1 ) in both fuel cell and electrolysis modes, with 600 h of stability in electrolysis mode (600°C, −0.5 to −2 A cm −2 ).