Design And Properties Of Sm_0.5A_0.5Fe_0.9Ni_0.1O_3-δ（A=Ca,Sr,Ba） Based Symmetric SOCs Electrode Materials

Solid oxide fuel cells（SOFC）are a clean and efficient energy conversion device.Symmetrical Solid Oxide Cells（SSOC）use the same ceramic oxide electrodes,which simplifies the cell manufacturing process and cost.The electrodes of the symmetric cell require good oxygen reduction reaction（ORR）and hydrogen oxidation reaction（HOR）in the Solid Oxide Fuel Cells（SOFC）mode,and good carbon dioxide reduction reaction（CO₂RR）and oxygen precipitation reaction（HOR）in the Solid Oxide Electrolysis Cells（SOEC）mode.This places high demands on the electrode materials.Doping at the A and B positions of perovskite can improve the conductivity and catalytic activity.Therefore,for this thesis,Sm Fe O_3-δwas selected and a series of studies were conducted on electrode materials doped with alkaline earth metals（Ca,Sr,Ba）at the A-site on the basis of Ni doping at the B-site.The electrochemical properties of these electrodes were also investigated.And their catalytic activity and stability were analyzed in comparison.Firstly,Sm_0.5Ca_0.5Fe_0.9Ni_0.1O_3-δ（SCFN）,Sm_0.5Sr_0.5Fe_0.9Ni_0.1O_3-δ（SSFN）and Sm_0.5Ba_0.5Fe_0.9Ni_0.1O_3-δ（SBFN）electrode materials were prepared by combustion method.SAFN-GDC/GDC/YSZ/GDC/SAFN-GDC symmetric cells were prepared using YSZ electrolyte prepared by the tape casting method as support for electrochemical performance study.The results of the half-cell impedance show that the impedance of SBFN-GDC half-cell under air is the smallest at 750°C with only0.25Ω·cm².SSFN-GDC had the best HOR activity,and the impedance of the half-cell was 1.26Ω·cm² under humid hydrogen atmosphere at 750°C.The peak power density of SSFN-GDC symmetric cell can reach 186.78 m Wcm^-2 at 750°C,which is better than SCFN-GDC symmetric cell and SBFN-GDC symmetric cell.The decay rates of SSOFCs with SCFN-GDC,SSFN-GDC and SBFN-GDC symmetrical electrode are7.39%,21.56%and 44.31%,respectively,when discharged at a constant voltage of 0.7V for 50 h at 700℃.Preliminary experiments show that SSFN has good electrocatalysis and stability.Then the electrolysis of CO₂ performance study was carried out along the SAFN-GDC/GDC/YSZ/GDC/SAFN-GDC symmetric cell structure.After treatment with high temperature CO₂ atmosphere,it is found that SCFN and SSFN generate carbonates,and SBFN is decomposed.The current density of SCFN-GDC symmetric cell can reach 625m Acm^-2 at 1.5 V working voltage at 800℃.In the open circuit state,the polarization impedance is only 1.3Ω·cm² at 800℃.The short and long-term test results show that the stability of SCFN-GDC symmetric electrolytic cell is better than SSFN-GDC and SBFN-GDC symmetric electrolytic cell.However,SCFN-GDC symmetric electrolytic cell cannot work continuously under the working voltage of 1.8 V,and the decay rate of 20 min is as high as 42.6%.Nor can it operate stably in the CO₂ atmosphere for a long time.Finally,the high-entropy perovskite material La_0.2Pr_0.2Sm_0.2Sr_0.2Ca_0.2Fe_0.9Ni_0.1O_3-δ（LPSSCFN）is designed and synthesized to improve the long-term stability of electrolysis CO₂.LPSSCFN can maintain its structure under high temperature CO₂atmosphere without carbonate generation.The electrolysis current density of LPSSCFN-GDC symmetric cell at 1.5 V applied voltage is 450 m Acm^-2 at 800°C.In the short and long term,the electrolytic cell is able to maintain good stability at the operating voltage,with only 9.3%degradation at 1.8 V applied voltage.The long-term stability is optimized compared to the SCFN-GDC symmetric cell.The thesis has 36 pictures,7 tables,and 115 references.