On the Stability Issues of TiO2-Based Composites in View of Fuel Cell Application: A Combined Experimental and Theoretical Investigation

Abstract

Oxide–carbonate composite electrolytes are complex materials whose peculiar conductivity performances are yet to be fully understood. Stability issues, however, arise when the carbonate is combined to an oxide such as TiO2, preventing practical fuel cell application of TiO2-based composites. To investigate the origin of such instability, a combined experimental and density functional theory-based approach is presented here and applied to the LiKCO3–TiO2 composite, focusing on energetic, electronic, and vibrational properties. The origin of the instability of this composite could be traced back to the intrinsic reducible nature of TiO2, with inserted Li being almost fully oxidized and stabilized by reduced Ti atoms at the oxide surface, thus facilitating LixTiO2 phase formation and accumulation close to the interface between the oxide and carbonate. This demonstrates that although the interface formation is critical for enhanced conductivity in YSZ- or CeO2-based composites, it is potentially responsible f...