Surface Superionic Conduction Enabled by In Situ Reaction‐Constructed Li ₂ TiO ₃ @TiO ₂ Core–Shell Interfaces for Low‐Temperature Solid Oxide Fuel Cells

ABSTRACT Insulating materials are essential for electron‐blocking functionality in low‐temperature solid oxide fuel cells; however, their intrinsic lack of efficient ion‐transport pathways severely limits electrochemical performance. Herein, an in situ phase‐transition strategy is employed to construct an epitaxial core‐shell structure electrolyte, enabling the formation of a surface superionic conductive layer and fundamentally resolving the problem of cell failure based on insulator electrolytes. During cell preheating, the solid‐phase transition of LiOH–TiO ₂ precursor induces the spontaneous self‐assembly of a unique Li ₂ TiO ₃ @TiO ₂ core–shell architecture, which establishes continuous three‐dimensional fast‐ion transport pathways along interfacial regions. Besides, experimental characterizations combined with density functional theory calculations indicate that the core–shell heterostructure dramatically enhances charge transfer kinetics via synergistic interfacial effects involving oxygen vacancy engineering, energy band alignment, and electron‐ion coupling. Consequently, fuel cells based on this electrolyte achieve an ion conductivity of 0.223 S/cm and a peak power density of 759 mW/cm ² at 550°C, while still maintaining an effective power output of 189 mW/cm ² at low temperature of 390°C. This strategy of in situ phase‐transition induced core–shell structure to achieve surface superionic conduction provides new opportunities for developing high‐performance solid‐state ion devices operating at low temperatures.