Mixed lithium-sodium (LiNaCO3) and lithium-potassium (LiKCO3) carbonates for low temperature electrochemical applications: Structure, electronic properties and surface reconstruction from ab-initio calculations

The structural, electronic and surface properties of the mixed lithium-sodium (LiNaCO3) and lithium-potassium (LiKCO3) carbonates were studied through periodic calculations performed at the density functional theory (DFT) level, using three different exchange-correlation functionals. The hybrid functional PBE0 was found to be the best one to describe both geometric and electronic features of bulk LiNaCO3 and LiKCO3. Polar (001) and non-polar (110) low index surfaces were taken into account, the first one being found the most stable in both cases, after reconstruction. Both introduction of vacancies (RI) and octopolar terminations (R-2) of (001), exposing Li ((001)(Li)) or Na ((001)(Na)) were described in detail. The computed stability order for the reconstructed surfaces in gas phase is: (001)R1Na > > (001)(R1)(Li) > (001)(R2)(Na) approximate to(Li)(R2). The obtained information, in particular regarding the electronic and surface properties, could be used in future to help understanding the role of mixed carbonates as component of oxide-carbonate electrolytes for low temperature solid oxide fuel cells (LT-SOFCs) applications, especially as reasonable starting points for dynamics calculations of liquid molten carbonates based systems. (C) 2016 Elsevier B.V. All rights reserved.