Strong immobilization of charge carriers near the surface of a solid oxide electrolyte

Abstract

A promise of nano-structured solid electrolytes (SEs) to present enhanced ionic conductivity necessary for low-temperature solid oxide fuel cell applications arises from the hypothesis that interfaces in these materials accelerate the ionic transport. However an in-depth knowledge of ionic dynamics in the interfacial regions, relative to the bulk, imperative to verify such a hypothesis is currently lacking. Here, we report the results of an atomistic study of oxygen-vacancy hopping dynamics in nano-crystalline Sc-doped ceria (SDC), one of the most studied oxygen-anion conducting SEs, using ⁴⁵Sc magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Our results provide direct experimental evidence that oxygen vacancies in the surface region of SDC are nearly immobile even at temperatures as high as 600 °C. Such findings suggest that accelerated oxygen-anionic transport along interfaces in SDC is highly unlikely, and thus lead to the conclusion that nano-structuring of this SE, and possibly other oxide SEs, will unlikely benefit their anionic conductivities.