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Er 0.2 Bi 0.8 O 1.5 (ESB), the oxide with the best oxygen conduction ability, is introduced to modify the electrical performance of Y 0.16 Zr 0.84 O 1.92 (YSZ) electrolytes for solid oxide fuel cells, and the electrical property and grain boundary conduction mechanism of xESB-YSZ (x = 0, 5, 10, 15, and 20 mol.%) are investigated. The introduction of ESB effectively promotes densification during sintering and improves the electrical performance of YSZ. At the addition of 20 mol.% ESB (20ESB-YSZ), the electrolyte allows a decrease of 500 °C for sintering temperature due to the low melting point of ESB, and ∼4 times higher electrical conductivity (0.093 S cm−1 at 750 °C) than that of YSZ (0.021 S cm−1 at 750 °C) without extra electronic conduction. Basing on the Motte-Schottky model, the enhance electrical performance is mainly attribute to two aspects. One is the lower space charge potential (0.014 V for 20ESB-YSZ, 0.207 V for YSZ), and the other is the higher impurity blocking term (0.97 for 20ESB-YSZ, 0.928 for YSZ). X-ray photoelectron spectroscopy analysis of composite electrolytes reveals that the oxygen vacancies content increase with the increased addition amount of ESB. The 20ESB-YSZ electrolyte-supported single cell with Ag-Sm 0.2 Ce 0.8 O 1.9 as electrodes exhibits a power density of 0.572 W cm−2 at 750 °C. • 20ESB-YSZ exhibits ∼4 times higher electrical conductivities than that of YSZ. • Grain boundary barrier of 20ESB-YSZ is ∼20 times lower than that of YSZ. • The impurity blocking effect of 20ESB-YSZ is reduced. • The electrolyte-supported single cell shows a maximum power density of 0.572 W cm−2 at 750 °C. [ABSTRACT FROM AUTHOR]