Preparation And Performance Research On The Electrode Of Sc₂O₃ Stabilized ZrO₂ Based Intermediate Temperature Solid Oxide Fuel Cells

The development of the intermediate temperature solid oxide fuel cells?IT-SOFCs?is a major research direction of SOFCs.In this study,the physical and electrochemical properties of Sc2O3-stabilized ZrO2?SSZ?based IT-SOFCs have been systematically investigated.The design of Ni-SSZ gradient anode structure improves the performance of SSZ based IT-SOFCs anode.Moreover,a novel Pr_0.6Sr_0.4FeO_3-?-Ce_0.9Pr_0.1O_2-??PSFO-CPO?composite cathode material has been developed and the PSFO-CPO nanofiber composite cathode is prepared by electrospun to improve the performance of the SSZ based IT-SOFCs cathode.The pure phase SSZ powder is successfully prepared by sol-gel method.The average particle size of SSZ powder is 90 nm and the specific surface area is 8.7 m2·g-1,which is suitable for the preparation of SSZ electrolyte by using tape casting method.SSZ green tape is sintered at different temperatures.With the increase of sintering temperature,the pores gradually reduce and the grains gradually grow up,resulting in the shrinkage and densification of SSZ green tape.The sample sintered at 1550 oC shows the highest flexural strength,up to 708 MPa.While sintering at much higher temperature would lead to a larger grain size and a lower flexural strength.The sample sintered at 1550 oC shows the highest conductivity,reaching 0.14 S·cm-1 at 800 oC.The single cell with the electrolyte sintered at 1550 oC shows the best discharge performance.The maximum power densities are 0.18,0.36,0.51 and 0.72 W·cm-2 at 650 oC,700 oC,750 oC and 800 oC,respectively.The anode-supported SOFCs with Ni-SSZ gradient anode has been successfully prepared by tape casting method and co-sintering technique.In order to optimize the sintering procedure,the thermal decomposition and sintering behavior of green tape are analyzed by the thermal gravimetric-differential thermal and thermal shrinkage tests.The gradient anode with pore size and porosity gradually increasing from internal layer to outer layer in anode can be obtained by controlling the content of pore forming additive.The internal layer anode with small pores and high specific surface area is helpful to provide more electrochemical reaction active sites.The outer layer anode with large pores and high porosity is more beneficial for the transmission of the fuel gas.The power densities of single cell with graded Ni-SSZ anode and cell with non-graded Ni-SSZ anode are 1.00W·cm-2 and 0.8 W·cm-2 at 800 oC,respectively.The electrochemical performance of single cell with graded Ni-SSZ anode is 25% better than the cell with non-graded Ni-SSZ anode.In order to simplify the cell preparation process,a Ni-SSZ/SSZ/LSM-SSZ single cell is prepared by using lamination method.What's more,optimizing the sintering procedure.In order to improve the performance of cathode,PSFO-xCPO?x=0-50 wt.%?have been successfully synthesized by a one-pot method.PSFO and CPO phases are formed after sintering at 1000 oC.The PSFO and CPO particles are uniformly distributed and interconnect with each other,which would provide more electrochemical reaction active sites.With the increase of CPO content in PSFO-xCPO,the conduction of oxygen ions increases in the cathode,which improves the electrochemical performance of composite cathode.The volume ratio of PSFO-40 CPO is close to the theoretical value 68:32,CPO particles connect with each other,can effectively improve oxygen adsorption and oxygen ionic conduction.While CPO content is excessive,the connectivity of PSFO decrease which result in the electron transport channels of PSFO are blocked and the decrease of electrochemical reaction sites.The GDC interlayer effectively reduces the mismatch of thermal expansion coefficients and prevents the chemical reaction between the PSFO-xCPO cathode and the SSZ electrolyte.There are no obvious diffusions of chemical elements at interfaces during SSZ electrolyte/GDC interlayer/PSFO-40 CPO cathode and decreases of discharge performance after 100 h stability testing.PSFO-40 CPO nanofibers composite cathode is synthesized by a one-step electrospin technique.PSFO and CPO phases are formed after sintering at 900 oC.The diameter of PSFO-40 CPO nanofiber is about 100 nm.The diameter range of PSFO and CPO particle is about 20-40 nm.High porosity cathode can be fabricated with inter-connected 3-D network of nabofibers,which supplies a “highway” for the transport of oxygen ion and the conduction of charge.As a result,the length of TPB is efficiently extended,and the performance of cathode is improved.The electrochemical performance of PSFO-40 CPO nanofibers structural cathode is higher than that of PSFO-40 CPO powder structural cathode,RP attains 0.072 ?·cm2 and 0.10 ?·cm2 at 800 oC,respectively.RP decreases by 28%.