Electrochemical Performance Of Cobalt Containing Cathode For Solid Oxide Fuel Cells

The solid oxide fuel cells have received considerable attention for their high energyconversion efficiency and low impact to environment as a mean of generating electricity.The current trend in SOFC developments is the reduction of their working temperatures,which can overcome many problems，such as electrode sintering，diffusion at interface anddifficulty in preparation of seals and interconnect at high temperature.At low temperatures,Co-based perovskite oxides have excellent electrochemical performance, especially,composite with cerium oxide electrolytes. At the same time, it is known that cobaltitesdisplay incompatible with standard electrolytes for their higher thermal expansioncoefficient(TEC). The misfit compound Ca3Co4O9allow a very good mechanicalcompatibility at the electrolyte interface for its thermal expansion closed to the TEC ofCGO. However, its electrochemical performance is poor at low temperatures. In this paper,electrochemical performance of the La0.7Sr0.3-xBaxCo0.8Fe0.2O3-δand Ca3Co4O9cathodeswas optimized by introducing oxygen ion conductor into the cathode material to formcomposite cathodes.The effect of Sm0.2Ce0.8O1.9dopant in composites on the electrochemical performanceon La0.7Sr0.3-xBaxCo0.8Fe0.2O3-δ-XSDC(x=0.1,0.15,0.2; X=20,30,40,50wt%) was studied.The results show that the composition with x=0.2shows the minimum area specificresistance. The change of SDC dopant has a significant effect on the electrochemicalproperties. At the temperature range of500oC to750oC, the polarization resistance isreduced with the increase of SDC dopant, and the composition with50%SDC shows theminimum area specific resistance, which is as low as0.06Ωcm2at750oC. The maximumpeak power density of the single cell with x=0.2composite cathode is1.006Wcm-2at650oC.To optimize the electrochemical performance of Ca3Co4O9cathode, the compositecathodes were fabricated on SDC electrolyte by impregnating aqueous solutionscorresponding to praseodymium doped ceria Pr0.2Ce0.8O2-δ(PCO) into the porous Ca3Co4O9 backbones. Pr0.2Ce0.8O2-δwith the different morphology feature was formed in Ca3Co4O9cathode skeleton by different solution impregnating process. Pr0.2Ce0.8O2-δnano-particleswere formed on Ca3Co4O9cathode skeleton by traditional solution imregnation andPr0.2Ce0.8O2-δnano-bar were formed on Ca3Co4O9cathode skeleton by solutionimpregnation combined with water hot process. The effects of cathode morphology oncomposite cathode polarization resistance were investigated. The results show that thecomposite cathode with Pr0.2Ce0.8O2-δnano-bar has lower polarization resistance than thecathode with Pr0.2Ce0.8O2-δnano-particles. The polarization resistance of composite cathodewith Pr0.2Ce0.8O2-δnano-bar shows the minimum area specific resistance, which is as low as0.46Ωcm2at750oC. The maximum peak power density of the Pr0.2Ce0.8O2-δnano-barcomposite cathode is0.533Wcm-2at650oC.