Functionally Graded IT-MOFC Electrolytes Based on Highly Conductive δ-Bi2O3-0.2 wt % B2O3 Composite with Molten Grain Boundaries

Recently, the concept of an intermediate-temperature molten oxide fuel cell (IT-MOFC) has been suggested. A MOFC combines the advantages of both the MCFC (highly conductive molten electrolyte) and SOFC (air oxygen is used as an oxidant). Here, we report the performances of IT-MOFCs based on functionally graded double-layer GDC/delta-Bi2O3-0.2 wt % Bi2O3 and YSZ/delta-Bi2O3-0.2 wt % Bi2O3 electrolytes in which delta-Bi2O3-0.2 wt % Bi2O3 composite with molten grain boundaries (GBs) on the cathode side (oxidant) provides the highest oxygen ionic conductivity of 2 S cm(-1) at 750 degrees C. The GDC or YSZ layer on the anode side (reductant) protects delta-Bi2O3-0.2 wt % Bi2O3 from decomposing in a reducing atmosphere. The optimal thicknesses of GDC and YSZ protective layers are evaluated. By reducing the thickness of the GDC and YSZ layers to 15 and 5 pm, respectively, the power density of these IT-MOFCs can theoretically reach a value of 1 W cm(-2). This value is significantly higher than the previously reported power output for IT-MOFCs based on the matrix TeO2-Te4Bi2O11 (11.5 mW cm(-2) at 640 degrees C) and Al2O3-Na2W2O7 (121 mW cm(-2) at 750 degrees C) electrolytes.