Research On Cobalt-free PrBa_0.5Sr_0.5Cu₂O_6-? Cathode Materials For Proton-conducting Solid Oxide Fuel Cells

Solid oxide fuel cells?SOFCs?,as a device that directly converts chemical energy into electrical energy,has the advantages of high energy conversion efficiency,small environmental pollution,and wide range of fuel application,making it one of the research hotspots.Compared with the conventional oxygen-ion conducting SOFCs?O-SOFCs?,the activation energy required for the electrolyte-conducting proton of the proton conductor SOFCs?H-SOFCs?is relatively low,so that the operating temperature of the proton conductor SOFCs is lower,which is more convenient for applications.As an important part of H-SOFCs,the cathode is very important to improve the output power of the battery.Therefore,the development of high-performance cathode materials has gradually become the one of the key points of research on H-SOFCs.The research focuses on the development of high-performance cathode materials and improvement on the output power of the single cells.The feasibility of using cobalt-free double perovskite PrBa_0.5Sr_0.5Cu₂O_6-??PBSC?materials as H-SOFCs cathodes was investigated and the single cells with PBSC composite cathodes were studied to obtain cells with better output performance and to understand the mechanisms involved.In Chapter 1,the concepts and working principles of SOFCs were briefly introduced.In addition,the current research background and significance of H-SOFCs are emphatically reviewed.In Chapter 2,the experimental details,such as the chemical reagents,sample preparation,characterization and testing methods etc.,were shown.In Chapter 3,the powder of cobalt-free PBSC was prepared using a citric acid-nitrate gel combustion process.The single cell NiO-BaZr_0.1Ce_0.7Y_0.2O_3-??NiO-BZCY?|BaZr_0.1Ce_0.7Y_0.2O_3-??BZCY?|PBSC was made to investigate the feasibility of using PBSC as H-SOFCs cathode.XRD test results show that PBSC calcined at 1000°C forms a tetragonal perovskite structure.The anode powder and electrolyte powder after calcination are all of pure phase.Electrochemical tests show that the polarization resistance of single cell NiO-BZCY|BZCY|PBSC is 0.42?·cm²at 750°C,the open circuit voltage of the cell of is 0.998 V and the peak power density is 230 mW·cm^-2,indicating that PBSC could be used H-SOFCs cathode material.The effects of the microstructure and the cathode/electrolyte interface on the performance of the battery were investigated by scanning electron microscopy.The thermal expansion coefficients of the cathode and the electrolyte were tested,and the thermal matching properties of the cathode and the electrolyte were analyzed.In Chapter 4,the proton-conducting composite cathode PBSC-BZCY and the proton-blocking composite cathode PBSC-SDC were prepared.The cells with PBSC-BZCY and PBSC-SDC as cathode were made to study the performance of the two composite cathodes.XRD results show that PBSC has good chemical compatibility with BZCY and SDC,after PBSC-BZCY and PBSC-SDC were calcined at 1000°C for 3 hours.The thermal expansion coefficients of PBSC-BZCY and PBSC-SDC are 12.5×10^-66 K^-1 and 13.7×10^-66 K^-1 respectively at 200-750°C,which are compatible with doped BaCeO₃ based electrolytes.The electrochemical performance of the single cell with PBSC-BZCY as the cathode shows that the open circuit voltage is 1.008 V,the peak power density is 669 mW·cm^-2,and the polarization resistance is 0.082?·cm² at 750°C.For the cell with PBSC-SDC as cathode,the open circuit voltage is 0.998 V,the peak power density is 914 mW·cm^-2,and the polarization resistance is 0.069?·cm² at 750°C.The performances of the single cells with PBSC-BZCY and PBSC-SDC were greatly improved compared with that of the cell with PBSC cathode,and the single cell with PBSC-SDC as cathode exhibits the best output power in the three cells,indicating good prospects in application in H-SOFCs.In Chapter 5,the thesis was summarized and the development of the proton conductor SOFCs and its future work were prospected.