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

Abstract

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 \({\text{P}}_{{{\rm{O}}_{{\text{2}}} }}\) with H2/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.