Study On Performance Optimization Of Electrloyte Materials For Proton-Conducting Solid Oxide Fuel Cells

Solid oxide fuel cells?SOFCs?have attracted more and more attentions due to their advantages in wide fuel adaptability,high energy conversion efficiency and low pollutant emissions.The proton conductor electrolyte materials have high proton conductivity at low-to-intermedium temperatures,and have low conduction activation energy compared to the oxygen ion conductor electrolyte materials.Compared with the oxygen ion conductor SOFCs,the water generate at the cathode in the proton conductor SOFCs,which can avoide the fuel gas dilution at the anode.Therefore,proton conductor SOFCs have been widely studied by researchers.At present,Doping BaCeO₃ and BaZrO₃ as the proton conductors are widely studied.This thesis studies the properties and performance optimization of these two electrolyte materials.The contents of each chapter of this thesis are as follows:In Chapter 1,this chapter focuses on the working principle of solid oxide fuel cells,the research status of electrolyte materials and the proton conductor transport mechanism.In Chapter 2,this chapter lists experimental reagents and equipment informations and the sample preparation and characterization methods have also displayed.In Chapter 3,the purpose of this chapter is to improve the proton conduction properties of BaCe_0.8Y_0.2O_3-?electrolyte materials by Nd and Y co-doping strategies.The results show that the BaCe_0.8Y_0.15Nd_0.05O_3-?component exhibits the highest conductivity in both air and hydrogen atmospheres.The results of XRD,SEM and impedance spectroscopy were used to explain the reasons for improving the performance of Nd and Y co-doping strategies.In Chapter 4,trivalent rare earth elements R and Y co-doping can improve the electrical conductivity of BaCeO₃ materials.To this end,in order to obtain improved performance of barium zirconate-based electrolyte materials,this chapter studied Sm and Y co-doped BaZr_0.8Sm_xY0._2-xO_3-??x=0,0.05,0.10,0.15,0.20?materials.The results show that with the amount of Sm increasing,the sintering properties of the materials enhance,the total electrical conductivity,grain boundary conductivity and grain conductivity decrease.A possible causes were used to analysis this phenomenon.In Chapter 5,calcium oxide as a sintering aid or calcium ion as a perovskite A-site dopant have been studied and the study of calcium ion as a perovskite B-site doping has not been reported in the literature.This chapter firstly studied the effect of low concentration calcium ion at B-site doping on the performance of BaZr_0.8Y_0.2O_3-?electrolyte.The results show that low concentration of calcium ions can be doped into the B-site of BaZr_0.8Y_0.2O_3-??BZY?and the sinterability of BZY is effectively improved.The sinterability improved and the free volume of the unit cell increased,which result in the conductivity of the BZYC5 higher than that of BZY.In Chapter 6,BaCeO₃-CeO₂ composite electrolyte can largely alleviate the instability of BaCeO₃ material and the leakage of CeO₂.In this chapter,the co-doping strategy was used to improve the conduction properties of BaCeO₃-CeO₂ composite electrolytes.Among the BCSY-SYDC complex oxygen ion-proton mixed conductors,this BaCeO₃ phase and CeO₂ phase have good chemical compatibility.BCSY-SYDC has higher conductivity and sintering activity while improving the disadvantages of BaCeO₃ and CeO₂.The anode-supported cells with BCSY-SYDC as the electrolyte have a higher open circuit voltage and a considerable power density than the CeO₂-based SOFCs under operating conditions.In Chapter 7,this chapter summarizes the whole thesis and looks forward to the future direction and goal of proton conductor research.