As hydrogen slowly becomes an increasingly popular carbon free energy vector; fuel cells, electrochemical devices able to convert H2 in electricity, gradually appear as a key component of the smart electrical grid of tomorrow. In particular, Solid Oxide Fuel Cells (SOFC) based on an oxygen ion conducting electrolyte are of special interest due to their very high yield in heat/electricity co-generation mode and the absence of noble metal on the electrodes. Yttria Stabilized Zirconia (YSZ), the dominant electrolyte used in SOFC does not allow high power output below 700 °C, driving the research efforts towards high temperature systems. However, durable and flexible high temperature SOFCs are extremely difficult to engineer due to the restrictions on materials set by the temperature range. A recently developed bi-layered electrolyte composed of stabilized ceria (GDC) and bismuth oxide (ESB) offers sufficient ionic conductivity to operate at temperatures as low as 350 °C, however there is still the need to find efficient cathodes to realize the full potential of this electrolyte. Hence, this proposal is focused on the search for new cathode materials and assembly procedures compatible with bi-layer GDC/ESB electrolytes. The goal of this project is to investigate the possibility of assembling solid oxide fuel cells using this new generation of bismuth based bilayer electrolytes, able to operate at temperatures of 400 °C and lower. We will focus on the design of cathode materials to be deposited on the “bismuth layer” of the electrolyte. For this purpose, we propose to look at the assembly of composite air electrodes made with materials with outstanding properties that are usually out of the scope of SOFC research due to chemical/mechanical compatibility. The considerably reduced temperature range will allow us to investigate oxides with metallic behavior such as high-Tc superconductors or SrFeO3-deta. High oxygen ionic conduction will be provided by structure deriving from delta-Bi2O3 such as ESB, DWSB or BiMeVOXs, usually not applicable to higher temperature range due to the reactivity and low melting point. Finally, the oxygen reduction catalytic properties of structures like LnBaCo4O7+delta and LnFe2O4+delta that are able to reversibly insert oxygen into the bulk of their structure at T < 400°C will be tested. By combining two materials with auspicious properties we hope to understand finely the parameters limiting the cathode performance at reduced temperature. To reach our goal an important work of characterization of the compatibility of the different phases of interest coupled to the measurement of their transport properties will allow the rational design of innovative electrodes specifically design to operate at reduced temperature. The performance of the electrodes will be evaluated on symmetrical cells using electrochemical impedance spectroscopy. Detailed understanding of the mechanisms impeding the low temperature operation of the air electrode will lead to electrode optimization. Ultimately these new compounds will be tested in full cell using GDC/ESB bi-layer electrolytes to demonstrate the full potential of these electrodes.