Ti/Fe Based Perovskite Symmetrical Electrode With High Electrochemical Performance For High Temperature Solid Oxide Cells

The working manner of high temperature solid cell is combining the solid oxide fuel cell?SOFC?and solid oxide electrolysis cell?SOEC?together.People can regulate the working state flexiblely according to their demand of electricity.When the demand for electricity is high,SOFC can directly convert chemical energy of fuel gas into electric energy.On the contrary,SOEC mode can make use of industrial waste heat and electricity to convert greenhouse gas such as carbon dioxide into fuel gas for cyclic utilization.This study researched symmetrical reversible solid oxide cell?SRSOC?.The symmetrical structure not only reduced the complexity in electrode preparation and assembly process greatly,but also cut down consumption cost.Additionally,the use of the same material as anode and cathode will also minimize compatibility problems caused by thermal expansion coefficient mismatch.In this dissertation,infiltration technique was used to introduce Ce_0.9Fe_0.1O_2-?and Ce_0.6Mn_0.3Fe_0.1O_2-?on the electrolyte backbone as barrier layer.Then the same method was used to introduce La_0.3Sr_0.7Ti_0.3Fe_0.7O₃?LSTF?on barrier layer to constitute the Ti/Fe based perovskite electrode.After optimization of the electrode preparation process,the electrochemical performances of the LSTF|CeFeO_2-?and LSTF|CeFeMnO_2-?electrodes under different working modes were investigated.The results in this dissertation suggested that the catalytic activity of LSTF|CeFeO_2-?electrode and LSTF|CeFeMnO_2-?electrode for fuel gas?H₂,syngas,CO or CH₄?were higher than that of LSTF electrode in SOFC mode.The addition of Mn can further improve the anode electrochemical performance.The highest discharge power densities of LSTF,LSTF|CeFeO_2-?and LSTF|CeFeMnO_2-?systems at 850 ^oC were 422.2?600.3?735.4 mW/cm² respectively,and comparing with the last one,the rate of increase reached 42%and 74%.The experimental results showed that the catalytic activities of the two systems for different fuel gas were in the same order,including H₂,syngas,CO and CH₄.Moreover,the polarization behaviors of the anode and cathode of the two systems in SOFC mode were studied by constructing a half-cell.The results showed that the anode was the key factor determining the polarization of the whole system.In SOEC mode,the catalytic activities for the reduction reaction of carbon dioxide of these two kinds of electrodes were compared.The results showed that the electrochemical properties of the two systems were far more than that of LSTF electrode.Also the catalytic activity of LSTF|Ce FeO_2-?electrode was a little higher than the other one.The results demontrated that the maximal current densities of LSTF|CeFeO_2-?,LSTF|CeFeMn O_2-?and LSTF at 1.4 V and 850 ^oC were 2.56,2.28 and1.84 A/cm²,being increased by 39%and 24%when compared with LSTF electrode.The short-term stability test at different vlotages also shown that barrier layer was beneficial to improve electrode stability.In reversible working mode,the experimental results showed that these two systems both had good reversibity.When they worked in SOFC mode,higher catalytic activity was achieved by LSTF|CeFeMnO_2-?.The maximum discharge power density of LSTF|CeFeMnO_2-?at 850 ^oC was 405.22 mW/cm² increased by 45%when compared with LSTF|CeFeO_2-?electrodes.Under the mode of SOEC,the overall electrochemical performances of the LSTF|CeFeO_2-?system were slightly higher than LSTF|CeFeMnO_2-?system,which is in agreement with the above conclusions.In a word,the two studied Ti/Fe-based perovskite electrodes LSTF|CeFeO_2-?and LSTF|CeFeMnO_2-?both had excellent electrochemical performance,especially LSTF|CeFeMnO_2-?electrode.As expected,by changing the doping amount of Mn and taking other modification methods,the in-depth exploration can be conducted to futher optimize its electrochemical performance.