Surface Superionic Conduction Enabled by In Situ Reaction-Constructed Li₂TiO₃@TiO₂ Core-Shell Interfaces for...

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-TiO₂ precursor induces the spontaneous self-assembly of a unique Li₂TiO₃@TiO₂ 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/cm² at 550°C, while still maintaining an effective power output of 189 mW/cm² 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.