Solid oxide fuel cells (SOFCs) are one of the most efficient electric power generating technologies through electrochemical reactions. However, conventional SOFCs based on yttria-stabilized zirconia (YSZ) electrolytes operate at high temperatures over 800 ºC, leading to high system cost and insufficient long-term stability. Reducing the operating temperature below 700 ºC brings significant reduction of system cost via scope expansion of material’s availability for stacks and balance of plants (BOPs), faster start-up time, as well as higher mechanical and chemical stability. However, the cathodic polarization loss at the electrolyte and cathode interface is significantly increased at reduced temperatures, due to the thermally activated nature of oxygen reduction reactions (ORRs). At below 700 oC, the erbia- stabilized bismuth oxide (ESB) is a promising electrolyte material due to exceptionally high oxygen ion conductivity. Moreover, recent studies showed that ESB improves the cathode performance via enhancing ORR rate at the electrolyte/cathode interface at lower temperatures (450 ~ 700 ºC)1,2. In this study, we employed an ESB interlayer at the interface between LSM-ESB cathode and YSZ electrolyte. The effect of the stabilized-bismuth oxide phase on ORR at reduced temperatures was systematically investigated by electrochemical impedance spectroscopy. Furthermore, I-V characterization was carried out to evaluate the performance of YSZ/ESB bilayered electrolyte SOFCs. Acknowledgement This research was supported by (1) Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2014R1A1A2057681), (2) the DGIST R&D Program of the Ministry of Science, ICT and Future Planning of Korea (1501- HRLA-01) and (3) the Global Frontier R&D on Center for Multiscale Energy System funded by the National Research Foundation under the Ministry of Science, ICT & Future Planning, Korea (2014M3A6A7074784). Reference 1. K. T. Lee, D. W. Jung, H. S. Yoon, A. A. Lidie, M. A. Camaratta and E. D. Wachsman, J. Power Sources, 220 (2012) 324–330. 2. K. T. Lee, A. A. Lidie, S. Y. Jeon, G. T. Hitz, S. J. Song and E. D. Wachsman, J. Mater. Chem. A, 1 (2013) 6199 Figure 1