Stable and high conductivity ceria/bismuth oxide bilayer electrolytes for lower temperature solid oxide fuel cells

A highly conductive bismuth oxide/ceria bilayer electrolyte was developed to reduce solid oxide fuel cell (SOFC) operating temperatures. Bilayer electrolytes were fabricated by depositing a layer of Er0.2Bi0.8O1.5 (ESB) of varying thickness via pulsed laser deposition and dip-coating on a Sm0.2Ce0.8O1.9 (SDC) substrate. The open-circuit potential (OCP) and ionic transference number (t(i)) of ESB/SDC electrolytes were tested in a fuel cell arrangement as a function of relative thickness, temperature, and PO2 with H-2/H2O and CO/CO2 on the anode side and air on the cathode Side. These EMF measurements showed a significant increase in OCP and t(i) with the bilayer structure, as compared to the cells with a single SDC electrolyte layer. Furthermore, improvement in the OCP and t(i) of bilayer SOFCs was observed with increasing relative thickness of the ESB layers. Hence, the bilayer structure overcomes the limited thermodynamic stability of bismuth oxides and prevents electronic conductivity of ceria-based oxides in reducing atmosphere.