Interfacial Nanostructuring Enables Integrated, Low‐Polarization Reversible Protonic Ceramic Cells

ABSTRACT Interfaces often impose the practical limits of protonic ceramic cells, where the oxygen electrode–electrolyte junction simultaneously governs polarization losses, tolerance to steam, and mechanical stability during reversible operation. Conventional porous electrodes typically rely on discontinuous point contacts and chemically reactive interfaces, which exacerbate interfacial resistance and promote delamination. Overcoming these coupled limitations requires an interlayer that is thin and conductive yet continuous, chemically compatible, and structurally integrated interlayer. Here, we report a pulsed laser deposition enabled interfacial nanostructuring strategy that forms a dense, nanocrystalline Pr 0.5 La 0.5 BaCo 2 O 5+δ interlayer directly on a chemically robust BaZr 0.8 Y 0.2 O 3 electrolyte. This interlayer establishes a conformal contact and a defect‐enriched reaction zone beneath a porous PLBC oxygen electrode, strengthening the electrode–electrolyte junction while preserving gas accessibility. The engineered interface increases interfacial bonding strength by threefold and substantially reduces interfacial polarization. As a result, the cells deliver peak power densities of 1.16 W cm − 2 at 600°C and exhibit stable steam electrolysis operation for ∼1000 h under 0.3–0.7 atm steam, maintaining steady operando impedance at 1.30 V with faradaic efficiency exceeding 92%. These results establish interfacial nanostructuring as an effective strategy to construct structurally integrated, low‐polarization electrode–electrolyte interfaces for versatile electrochemical devices.