A New Double Doped Bismuth Oxide with Stable Ionic Conductivity at Intermediate Temperatures

Abstract

Pure bismuth oxide exhibits the highest oxygen ion conductivity of any known material from approximately 730°C up to the melting point. While the highly conductive FCC cubic phase of Bi2O3 can be stabilized to room temperature by doping the structure, the conductivity ultimately suffers at intermediate temperatures due to the oxygen subblattice ordering. Traditional bismuth oxide based electrolytes are not suitable in solid oxide fuel cells that operate below approximately 600°C because of the ordering phenomenon. Reported herein is a Bi2O3 electrolyte material that does not order below 600°C. At temperatures that range from 400°C up to 550°C the electrolyte material does not exhibit noticeable degradation of conductivity, even after annealing for hundreds of hours. Although the oxygen ion conductivity of the material is not equivalent to FCC cubic Bi2O3, it maintains superior conductivity to other prominent SOFC electrolytes such as GDC, SNDC, and YSZ. Furthermore the highly conductive and stable bismuth oxide material also works in a composite cathode alongside LSM. This dual bismuth based electrolyte and cathode design allows for a stable performing SOFC that can operate at intermediate temperatures.