A simple bilayer electrolyte model for solid oxide fuel cells

A simple electrolyte model for bilayer ion-conducting membrane used in solid oxide fuel cell (SOFC) was developed. The model considers yttria-doped bismuth oxide (YDB) and gadolinia-doped ceria (GDC) as the substrate electrolyte, both coated with a thin layer of yttria-stabilized zirconia (YSZ) on the anode side. Migration of oxygen ions and diffusion of free electrons and electron holes through the bilayer electrolyte form the basis of modeling in this study. Results showed that depositing a very thin layer of YSZ onto the substrate electrolyte in the thickness ratio of 1 to 10,000 could increase the interfacial oxygen partial pressure significantly in the bilayer electrolyte and reduce the penetration of electronic current. The improved interfacial oxygen partial pressure by YSZ coating, higher than the equilibrium partial pressure of Bi/Bi₂O₃, made bismuth oxide a possible candidate for use in SOFC. An important result of the electronic blocking effect with bilayer electrolyte SOFC is to improve the open circuit voltage and thus to enhance the output power density of the cell.