Preparation And Performance Research Of Oxygen Electrode Materials For Proton Conducting Solid Oxide Electrolysis Cells

The rapid growth of the world economy and the continuous burning of fossil energy have resulted in a significant increase in the global demand for clean,renewable and sustainable energy.Hydrogen is a clean fuel and the solid oxide electrolysis cell（SOEC）hydrogen production based on fuel cell technology has outstanding advantages such as cleanliness,high efficiency,energy saving and environmental protection,which has received extensive attention in recent years.Compared with traditional oxygen-ion-conducting solid oxide electrolysis cells（O-SOEC）,proton-conducting solid oxide electrolytic cells（H-SOEC）has higher ion conductivity and lower activation energy of proton conductors at a relatively low temperature,so its operating temperature is lower than O-SOEC,which can provide a wider range of material options for H-SOEC system components to reduce manufacturing costs.However,the current development of H-SOEC lags far behind O-SOEC,which is mainly due to the limitations of materials and catalyst technology,including thin electrolyte layer stabilization technology,oxygen electrode and fuel electrode catalyst technology with high catalytic activity and stability.The research focuses on the development of high-performance and high-stability H-SOEC oxygen electrode,and different material development strategies are used to prepare different oxygen electrode materials.Research on oxygen electrode materials with triple conductivity of protons,oxygen ions and electrons(H⁺,O^2-and e^-),based on the triple-conducting oxide Pr₂Ni O_4+δ（PNO）,the layered perovskite(Pr_0.9La_0.1)₂(Ni_0.8Cu_0.2)O_4+δ（PLNCu）was prepared by doping La at the A site and Cu doping at the B site to improve its stability and sintering activity.At the same time,Sr_0.9Fe_0.8Sc_0.1Co_0.1O_3-δ（SFScC）oxygen electrode material was prepared based on the traditional material Sr_0.9Fe_0.9Co_0.1O_3-δ（SFC）and modified by Sc ion doping.The influence of Sc³⁺doping on the electrochemical performance of SFC-based oxygen electrode was studied.Through the characterization of the physical and chemical properties of the above-mentioned oxygen electrode materials,and the test results of half-cell and single cell preparation based on the oxygen electrode materials,the electrocatalytic performance of the oxygen electrode and its application in H-SOEC are comprehensively analyzed.The main results obtained in the thesis are as follows:（1）The PLNCu oxygen electrode material with tetragonal P4₂/ncm K₂Ni F₄ perovskite structure was synthesized.Through XRD refinement,it is found that the lattice parameters of PLNCu are a=b=5.49（1）（?）,c=12.17（2）（?）.The average thermal expansion coefficient of PLNCu is 13.78×10-6 K-1（40-800℃）,which matches the proton conductor electrolyte.XPS results show that PLNCu has a high proportion of surface oxygen vacancies,which helps to improve the catalytic activity of the material.At the same time,the doping of Cu can effectively improve the conductivity of PLNCu.（2）The activation energy of the PLNCu-BZCY composite oxygen electrode is 1.42 eV,the polarization resistance of a single cell at 750℃ is as low as 0.056Ω·cm²,and the electrolysis current density at 1.3 V is 1.61 A·cm^-2.A 100-hour long-term stability test was performed on a single cell,and the results showed that the cell performance and structure remained stable.（3）The crystal structure of SFC and SFScC synthesized by solid phase method is cubic Pm-3m perovskite structure,which has good chemical compatibility with the electrolyte BZCY.Sc³⁺doping can significantly reduce the thermal expansion coefficient of SFC and enhance the water absorption of the material,but it will reduce conductivity.XPS analysis found that the oxygen vacancy concentration of Sc³⁺doped SFScC is higher,but the doping of Sc³⁺may promote Sr surface segregation,which is not conducive to the long-term stability of the oxygen electrode.（4）The activation energy of SFScC electrode is 0.96 eV,which is lower than 1.04 eV of SFC electrode.At 750℃,the highest power density of SFScC single cell in SOFC mode is 1W·cm^-2,which is much higher than 0.83 W·cm^-2 of SFC single cell.In SOEC mode,the electrolytic current densities of the SFScC single cell at 750℃,700℃,and 650℃ in 1.3 V are1.784 A·cm^-2,0.76 A·cm^-2,0.48 A·cm^-2,respectively.Sc³⁺doping can improve the catalytic activity of SFC and thus improve the electrochemical performance of the cell.