Metal oxides with oxygen vacancies are widely used in electrochemical processes at high temperature due to their ionic conductivity. These processes are strongly influenced by the electrostatic potential of the ions because it is closely related to the electrochemical potential. We calculate the partial molecular Coulomb internal energy for different compositions of yttria-stabilized zirconia (YSZ) with molecular dynamics (MD) at different temperatures and zero pressure. On the basis of thermodynamic considerations, we assume that these quantities correspond to the electrostatic potential of ZrO 2 and Y 2 O 3. We also calculate the mean electrostatic potential of the ions and develop a mixing rule between this potential and the electrostatic potential of the molecules. With this mixing rule and following the thermodynamic framework proposed in this study, one can calculate the Coulomb contribution of other thermodynamic properties like the entropy or the Nernst–Planck diffusivities for YSZ-like metal oxides. Furthermore, the methods proposed here can be extended for other electrolyte mixtures.