A new solid oxide fuel cell design based on thin film electrolytes

A novel solid oxide fuel cell (SOFC) design that can be fabricated entirely using low-temperature, thin-film processing is described. Potential advantages of the cell are reduced materials costs and improved fuel-cell characteristics. The critical design feature is the use of thin (≈ 50 nm), catalytically-active oxide layers on a < 10 μm thick yttria-stabilized zirconia (YSZ) supported electrolyte to minimize reaction overpotentials and ohmic losses. Doped ceria at the fuel electrode side and doped bismuth oxide at the oxygen electrode side are proposed for the surface layers. The surface reaction rates and overall electrolyte conductance in this design are high enough at < 750 °C to allow efficient SOFC operation. This operating temperature is low enough that low-resistance, thin-film metal electrodes, Ni at the fuel side and Ag at the oxygen side, can be used to provide low ohmic losses. The overpotential behavior of the proposed cell is estimated on the basis of literature data and leads to fuel efficiencies > 50% at a power density of ≈ 0.5 W/cm2 when operated at 750 °C. The thin film monolithic design will lead readily to the incorporation of the cells into stacks with high power-to-weight and power-to-volume ratios. Methods for cell fabrication are discussed.