Preparation And Study Of Nb And Cu Codoped SrCoO₃ As Cathode Material For Intermediate And Low Temperature Solid Oxide Fuel Cell

Solid oxide fuel cells as an electrochemical energy conversion devices has attracted much attention in recent years.Reducing the operating temperature is the current trend.The key is to develop cathode with high oxygen reduction reaction activity at low and intermedium temperature.In this study,SrCoO_3-?is used as the parent material,and Nb and Cu are co-doped at the B site to obtain SrCo_0.95-x.95-x Nb_0.05Cu_x O_3-??SCNC,x=0²0%?.The 5%Nb stabilize SrCoO_3-?a cubic phase,neither the doping of Cu.The structure and properties of SrCo_0.95-xNb_0.05Cu_xO_3-?at low temperature cathode for SOFC is evaluated.SCNC is synthesized by the solid state reaction method.XRD shows that all SCNC powders have a cubic phase.As the Cu content increases,the unit cell parameters increase gradually,but the crystal symmetry gradually decreases.The average particle size increase with Cu content increasement.According to O₂-TPD and thermal expansion behavior,the high-valent of Co ions and Cu ions reduce to low valence at high temperature,but the occurrence of the reduction is suppressed by the Cu co-doping,leading to a decreasing of thermal expansion coefficient.The thermogravimetric and iodometric titration analysis show that the oxygen vacancy concentration increased rapidly with the increasement of Cu,that the?of SrCo_0.85Nb_0.05Cu_0.1O_3-?is 0.368,compared with that of 0.308 for SrCo_0.95Nb_0.05O_3-?.XPS shows that Co is+3 and+4 in SrCo_0.85Nb_0.05Cu_0.1O_3-?,and Cu is+1 and+2.The average valence of the B site of SrCo_0.85Nb_0.05Cu_0.1O_3-?at room temperature was2.653 by quantitative calculation of the peak area.Although Cu doping reduces cell symmetry,the polarization impedance of the cathode is greatly reduced at both high and low frequencies.The polarization impedance of SCNC10 is as low as 0.02?cm² at 700°C,and the activation energy of the reaction is only 0.78 eV,which is much lower than that reported in the literature.The reaction order m is 0.32 of SrCo_0.85Nb_0.05Cu_0.1O_3-?together with the relaxation time distribution analysis indicate that the rate determine step may be a charge transfer reaction.The electronic conductivity is as high as 550 S cm^-1 at 400°C,and the peak discharging power density is about 900 mW cm^-2 at 850°C,compared with400 mW cm^-2 of SrCo_0.95Nb_0.05O_3-?.The doping of 10%Cu increase the discharging power density by 2 times than that of SrCo_0.95Nb_0.05O_3-?,proving the excellent performance of SrCo_0.85Nb_0.05Cu_0.1O_3-?.SrCo_0.95Nb_0.05O_3-?,SrCo_0.85Nb_0.05Cu_0.1O_3-?were combined with 30 wt%GDC,respectively.SrCo_0.85Nb_0.05Cu_0.1O_3-?has good compatibility with GDC electrolyte,which significantly improves the thermal expansion properties of the material.These demonstrate that SrCo_0.85Nb_0.05Cu_0.1O_3-?is a promising cathode materials for SOFCs operating at low and intermedium temperature.