It is necessary to elucidate the correlation between hydration properties and proton distributions in electrolytes as proton conductors to allow for further improvements in solid oxide fuel cells. In this study, the hydration properties of Sc-doped BaZrO3 (BZO) were investigated by means of density functional theory calculations capable of taking both the local structural configurations and the hydration levels into account. At a low hydration level, Sc-doped BZOs gained a negatively larger hydration energy, that is, more exothermic reaction, by incorporating an H2O molecule with unstable oxygen vacancies adjacent to Zr. At a high hydration level, the configuration of ScO4(OH)2, which has a positive net charge as a local structure, was formed with a smaller but negative hydration energy by the reaction of H2O with oxygen vacancies adjacent to Sc. This indicates that the stability of the whole system, and not only the local electrostatic interactions of point defects, needs to be taken into account when considering the hydration energy. The characteristic local structure of ScO4(OH)2 was identified using 45Sc nuclear magnetic resonance (NMR) chemical shift calculations. It is proposed that the resolution of current 45Sc NMR spectroscopy techniques does not allow for the detection of ScO4(OH)2 in Sc-doped BZOs and that a higher resolution 45Sc NMR technique will likely reveal the existence of ScO4(OH)2.
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