Preparation Of The Novel Cathodes And The Application In Proton-Based Solid Oxide Fuel Cells

Solid oxide fuel cells(SOFCs)have attracted more and more scientists’ attention due to their advantages such as low cost,simple structure,and zero pollution emission.In the early years,the operating temperature of SOFCs was high,which not only could increase the costs,but also be harmful to their stability.Therefore,reducing the operating temperature of SOFCs becomes a huge challenge.Lowering operating temperature can cause the ohmic resistance and polarization resistance of the cell to increase sharply,reducing the performance of the cell.This thesis aims to develop low-or medium-temperature solid oxide fuel cells.It focuses on designing and researching suitable proton-based SOFCs.In this work,ideal cathode materials of SOFCs have been obtained,wich have high electrocatalytic activity and suitable for applying at low and medium temperatures.In Chapter 1,the concepts,the reaction principles of O-SOFC sand P-SOFCs and the differences between them are introduced.Then we focus on the electrolyte materials and cathode materials on P-SOFCs in recent years.In Chapter 2,a series of cubic perovskite materials,BaC0xFe0.7-xZr0.3O3-δ(0.2≤x≤0.5)(BCxFZ),were successfully prepared.In this chapter,we studied the changes in the conductivity,thermal expansion of the cathode material and the performance of the cell in P-SOFCs by adjusting the ratio of Co and Fe of the cathode.In addition,the theoretical calculation and analysis of the oxygen vacancy formation energy and the proton hydration energy of the cathode material are also performed through the first-principles calculation.Finally,CO2/H2O stability was tested on the cathode materials and long-term stability of the cell was tested.When the Co content is 0.4,the cell has the largest output power density and the smallest polarization resistance,with 679 mW/cm2 and 0.067 Ω cm2 at 700℃.It can be seen that the higher the Co content,the performance of the cell is not better.It can be analyzed through theoretical calculations.This is because when the Co content exceeds a certain value,the proton conductance of the cathode material decreases,which is not conducive to its application in proton-based SOFCs.In Chapter 3,a BaFe0.8Zr0.1In0.1O3-δ(BFZI)cathode was designed and successfully prepared,and a BaFe0.9Zr0.1O3-δ(BFZ)cathode was used for comparison.The interplanar spacing,electrical conductivity,and hydration capacity of two cathode materials were analyzed.In addition,the cathode materials were tested by XPS.And two kinds of cathode materials are applied to P-SOFCs.The results show that at 700℃,the cell with BFZI has higher output power density and smaller polarization resistance,1023 mW/cm2 and 0.025 Ω cm2.It can be seen that although the conductivity of cathode is decreased after the doping of indium ions,the hydration ability of the cathode material and the ORR activity are both enhanced,which can help to improve the performance of the cell.In Chapter 4,the anode containing Ba source was applied to Nd-doped SDC.Sintering at high temperature helps Ba ions to diffuse to the interface between the electrolyte and the anode to form an electronic barrier layer,which effectively solves the problem-internal electronic short circuit of the cerium oxide-based SOFCs.The open-circuit voltage of cell has been increased dramatically,1.03 V at 650℃.At this time,the maximum output power density reached 1024 mW/cm2.Compared with SDC without Nd,SNDC has higher oxygen ion conductivity and higher oxygen doping rate.Therefore,the cell with SNDC not only have smaller ohmic resistance,but also have smaller polarization resistance,which can improve the performance of the cell.The fifth chapter summarizes the whole paper and looks forward to the future of SOFCs.It also puts forward several issues that this paper can continue to study.Finally,the writer expresses her gratitude to the mentor,classmates and family.