The stabilization of the cubic phase arises from applied lattice strain due to the presence of large cerium ions on the host lattice sites . This substitution assists formations of the highersymmetry cubic phase by lowering the 𝑐/𝑎 ratio in the tetragonal phase, thus resulting in higher ionic conductivity . Since the cubic (fluorite) structure attracts the most interest for investigation, numerous studies have been done on the influence of the microstructure and lattice strain on the ionic conductivity of the cubic phase of the SSZ . However, there are still regions that have been only poorly investigated within the tetragonal crystal structures in the 𝑆𝑐 ! 𝑂 " -𝐶𝑒𝑂 ! -𝑍𝑟𝑂 ! system. Enhancement of the mechanical properties in 6 mol% scandia-1 mol% ceria-doped zirconia (herein 6Sc1CeZr), compared to 10 mol% scandia-1 mol% ceriadoped zirconia (10Sc1CeZr), in addition to the 40% lower production cost due to a reduction in expensive 𝑆𝑐 ! 𝑂 " , make 6Sc1CeZr an attractive candidate for investigation in SOFCs applications as well as solid oxide electrolyzer (SOECs). To the best of the authors' knowledge, while 6Scstabilized zirconia (6ScSZ) and 10Sc1CeZr has been the subject of massive investigations, the electrochemical performance of the 6Sc-1Ce-co-doped zirconia has remained unexplored. Much research on 10Sc1CeZr has also revealed that although 10Sc1CeZr is highly conductive, the system is exposed to form 𝛽-rhombohedral phase which dramatically exacerbates the conductivity . Also high contents of scandia results in formation of local defects trapped in oxygen vacancies and reduces the oxygen-ion conductivity where Chen et al. find that the probability of having a trapped site is given by the Fermi-Dirac statistics. Moreover, all active electrochemical devices are prone to electrochemically-induced degradation due to unbalanced chemical gradient potential of the mobile species . It has been theoretically and experimentally studied that actual oxygen chemical potential inside the solid electrolyte can be increased or decreased compared to corresponding values at the electrodes in active current carrying devices in electrolysis mode . Addition of dopants with multiple oxidation states, such as the addition of 1 mol% ceria to zirconia, is able to introduce some electronic conductivity and decrease the polarization resistance in ionic conductors and slow down the degradation rate by partial random ceria reduction where 𝐶𝑒 &% + 𝑒 ↔ 𝐶𝑒 "% . Furthermore, Shobit et al. observed that co-doping of scandia-stabilized zirconia with ceria also contributes to the formation of highly-symmetric fluorite phase, lowering the c/a ratio in tetragonal phase, and enhancing total conductivity.