Performance Of BaCo_0.4Fe_0.4Zr_0.2-xY_xO_3-δ As The Cathode Material For LT-SOFCs

Because of their instrinsically high efficiency,low emissions and fuel flexibility,solid oxide fuel cells（SOFCs）are believed to be one of the most promising clean power generation devices for the future.Poor cathodic performence at intermediate to low temperature,however,has become the main obstacle to realize the implemention of SOFCs technology into commercial application.So searching for an excellent low temperature solid oxide fuel cell（LT-SOFCs）cathode catalyst for oxygen reduction is still the research focus.In this paper,both BaCo_0.4Fe_0.4Zr_0.2O_3-δ（BCFZ）and BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ（BCFZY）doped perovskite powders were synthesized by combined EDTA-citrate complexing sol-gel process which is one of the wet chemical methods.The formation of both single perovskite oxides with cubic symmetry was demonstrated by X-ray powder diffraction（XRD）technology.And the XRD patterns of BCFZ-SDC（and BCFZ-BZCYYb）and BCFZY-SDC（and BCFZY-BZCYYb）mixtures after calcination at 1050℃indicated that the cathode materials BCFZ（BCFZY）were chemically compatible with the commonly used electrolyte materials such as Ce_0.8Sm_0.2O_1.9（SDC）and BaZr_0.1Ce_0.7Y_0.1Yb_0.1O₃（BZCYYb）.Then for BCFZ and BCFZY materials,scanning electron microscopy was used to characterize their particulate morphology.Four-probe method was employed to test the electrical conductivity in air at temperatures between 300℃and 800℃.The thermal expansion data was collected in air from room temperature to 1000℃.Oxygen temperature-programmed desorption（O₂-TPD）was performed,thermogravimetric analysis was given and electrochemical performance of both materials as cathodes of LT-SOFCs was also explored.First,BCFZ and BCFZY were used respectively as the cathode materials of oxygen ion-conducting solid oxide fuel cells（O-SOFCs）with SDC as the electrolyte,then the anode-supported single cells Ni-SDC∣SDC∣BCFZ（with electolyte 32μm in thickness）and Ni-SDC∣SDC∣BCFZY（with electolyte 33μm in thickness）were prepared.Under the same conditions to investigate their output performance and measure their electrochemical polarization resistance.Ni-SDC∣SDC∣BCFZ achieved maximum output power densities in the range of 650℃⁵00℃,which were 620.07,536.04,426.04,286.87 mW/cm².And its polarization resistance values were 0.041,0.058,0.099,0.198Ω·cm²at corresponding temperatures.The maximum power densities ofNi-SDC∣SDC∣BCFZY could reach1340.55,1068.47,775.84,497.44 mW/cm² from 650℃to 500℃,corresponding polarization resistance values were 0.017,0.028,0.056,0.124Ω·cm².The result indicates that BCFZY possesses better performance than BCFZ in O-SOFCs.Then BCFZ and BCFZY were used respectively as the cathode materials of proton-conducting solid oxide fuel cells（H-SOFCs）with BZCYYb as the electrolyte,the anode-supported single-cells Ni-BZCYYb∣BZCYYb∣BCFZ（with electolyte 26μm in thickness）and Ni-BZCYYb∣BZCYYb∣BCFZY（with electolyte 35μm in thickness）were prepared.The cells were also adopted in the same conditions for evaluating their electrochemical performance and output power.At 700℃⁵00℃operating temperatures,the maximum output power densities of Ni-BZCYYb∣BZCYYb∣BCFZ were 441.15,389.13,348.67,289.07,234.11 mW/cm².Corresponding polarization resistance value were 0.055,0.094,0.184,0.349,0.701Ω·cm².Higher maximum power densities of 653.29,600.59,521.61,433.55,338.34 mW/cm² were obtained for cell Ni-BZCYYb∣BZCYYb∣BCFZY than that of BZCF,lower polarization resistance were also showed 0.016,0.023,0.040,0.087,0.210Ω·cm².It is described that BCFZY is more suitable for the cathode of H-SOFCs than BCFZ.It can be seen that BCFZY has superior electrochemical performance as cathode material of LT-SOFCs,which is comparable to its relatively high oxygen vacancy concentration and the significant feature that its lattice oxygen is easy to desorption at low temperature.The results show that BCFZY has a wider development prospect in the application of low temperature oxygen ion conductor solid oxide fuel cells.