Research Of Efficient Utilization For Carbon Fuel And CO₂ Based On Solid Oxide Cells

The rapid increase of energy consumption by human society leads to the serious shortage of fossil energy.Meanwhile,social activities such as excessive exploitation and uncontrolled burning of fossil fuels have seriously damaged the ecological balance.Because of its high energy density and low pollution output,biomass energy has been widely studied and applied around the world as an alternative energy source of fossil fuels to solve the problems of human development and living environment,and to achieve the dual carbon target of carbon peaking and carbon neutrality with high quality and efficiency while promoting social development.Solid oxide cell（SOC）is a kind of all-solid energy conversion device with high energy conversion efficiency.Through the development of electrode materials and microstructure,it can be directly applied to carbon containing fuel represented by biomass energy to accelerate its development and utilization.SOC has two operating modes:solid oxide fuel cell（SOFC）and solid oxide electrolysis cell（SOEC）.At present,the direct use of carbon-containing fuel and carbon conversion SOC face the following challenges:the ability to resist carbon deposition and sulfur poisoning is weak,low conductivity of materials,and electrolyte compatibility and matching degree,etc,the above problems will lead to rapid deactivation of SOC devices and unsatisfactory operating efficiency in practical applications.In order to solve the above problems,this paper carried out relevant research on the carbon deposition resistance of SOC,catalytic reforming of fuel and ion reaction mechanism by micro-reconstruction of electrode materials,external processing of interface structure.The SOFC which uses the structural stability of ABO₃-type perovskite SrTiO₃ was exploited to increase the redox reaction site by doping the variable valence Mn^4+/3+2+in B site of SrTiO₃ to improve the catalytic performance of carbon fuels.The doping limit of manganese in SrTiO₃ is generally low in order to prevent the overall crystal structure instability brought about by the variation of Mn^4+/3+2+,but the additional Pr^3+/4+donor doping on Sr site of SrTi_0.5Mn_0.5O₃ was found to enhance the structure stability,electric conductivity,electrocatalysis of perovskite.Since Pr_0.5Sr_0.5Ti_0.5Mn_0.5O₃ has excellent electrochemical properties under high temperature redox conditions,it can be used as the cathode and anode of symmetric solid oxide fuel cell（SSOFC）,and the use of identical electrodes for both cathode and anode can simplify the preparation process and increase the durability of the cell.The cell with Pr_0.5Sr_0.5Ti_0.5Mn_0.5O₃ electrode excels under H₂,propane or CH₄/H₂ fuel providing co-catalyst was infiltrated in the anode side.The polarization resistance value of SSOFC also using Pr_0.5Sr_0.5Ti_0.5Mn_0.5O₃ as cathode was 0.27Ωcm²,and 0.33Ωcm² for the SSOFC using H₂ fuel.The performance under CH₄/H₂ fuel can be boosted to above0.9 Wcm^-2 if Ni/ceria was loaded on to the anode to enhance the methane reforming.This work contributes to a perovskite anode with high Mn doping in SrTiO₃ for the application in SSOFC for natural gas with renewable H₂injection.The SOEC which uses carbon dioxide for electrolytic conversion,can improve the conversion rate of carbon dioxide limited by thermodynamic stability by improving the application way of carbon dioxide,and further promote the technological progress of industrial carbon conversion and the realization of dual carbon target on the basis of using biomass energy.Based on the principle that multiple active sites can accelerate the electrochemical reaction and transformation,perovskite oxide titanate Pr_0.35Sr_0.5Ti_0.5Mn_0.45X_0.05O_3-δ（X=NiCoCu）with multiple active sites was synthesized by solid phase method by creating defect sites at site A and doping transition metal at site B.Pr_0.35Sr_0.5Ti_0.5Mn_0.45X_0.05O_3-δwas applied to the SOEC in electrolytic CO₂ under 800 ℃ for the work because of the good performance in thermal stability and electrochemical tests.Although the current density(0.83 A cm^-2)of the SOEC with Pr_0.35Sr_0.5Ti_0.5Mn_0.5O_3-δas fuel electrode was lower than that of the Pr_0.35Sr_0.5Ti_0.5Mn_0.45Ni_0.05O_3-δ(2.0 A cm^-2)during the CO₂ electrolysis process,its operation time reached an unexpected 82 hours.In addition,the microstructure analysis of the electrode also found that there was obvious metal particles which were clear and evenly distributed on the surface of perovskite.The results showed that perovskite oxides with both A-site defects and B-site transition metals had excellent electrolytic ability and high stability,and had broad prospects as electrolytic electrode materials for promoting carbon conversion through direct use of CO₂.