Modeling composite electrolytes for low-temperature solid oxide fuel cell application: structural, vibrational and electronic features of carbonate-oxide interfaces

We present a combined experimental and theoretical investigation of the YSZ-LiKCO3 composite, as an electrolyte alternative for low-temperature solid oxide fuel cells (LT-SOFC). Insights on its structure, stability, and electronic and vibrational properties are presented and discussed. The large adhesion energy computed (3.19 eV) indicates a strong interaction between the two phases, which has two main origins: adsorption of the ionic species of the salt on the oxide surface and minimization of the elastic strain due to the lattice mismatch between the two surfaces, resulting in a disordered amorphous-like state for the carbonate phase in agreement with the experimental observations. The material shows a band gap of 5.78 eV, very close to the one of pure YSZ and a major ionic character for the ion-ion interactions between YSZ and LiKCO3, with a slightly higher covalent contribution in the case of the adsorption of CO32- groups on the oxide surface sites. Computed IR and Raman spectra showed an overall very good agreement with the measured experimental data, validating the proposed interface model, which is an important first step towards the modelling of transport mechanisms at the interface between oxides and carbonates in composite electrolytes in order to better understand their peculiar properties and to provide useful guidelines to design novel compounds with improved performances.