Theoretical and experimental study on a fast proton transport pathway in CeO₂-coated SrTiO_3-δ through surface vacancy...

Overcoming the high-temperature limitations of ceramic fuel cells (CFCs) requires the development of electrolytes capable of efficient proton transport at reduced operating temperatures. In this work, we introduced a surface-engineered SrTiO_3-δ electrolyte coated with 10 mol%-CeO₂, forming a core-shell heterostructure that promoted the formation of oxygen vacancies localized at the interface. These vacancies significantly reduced the energy barrier for proton migration, enabling enhanced ionic conductivity at low operating temperatures. The 10 mol%-CeO₂-coated SrTiO_3-δ exhibited a high ionic conductivity of 0.14 S cm^-1 and delivered a peak power density of 0.81 W cm^-2 at 550 °C. Isotopic substitution and proton-blocking membrane experiments confirmed a dominant protonic conduction mechanism, contributing up to 78 % of the total power-output. Density functional theory calculations revealed that the CeO₂ coating layer lowered the oxygen vacancy formation energy to 3.7 eV and facilitated charge redistribution favorable to proton transport. This work established a scalable and cost-effective surface modification strategy to realize high-performance electrolytes for low-temperature CFCs, surpassing conventional bulk doping approaches in both conductivity and electrochemical output.