Electrochemical Performance Of(La_0.3Sr_0.7)_1-xTi_0.3Fe_0.7O_3-? Symmetrical Electrode For Sofcs Based On A Site Deficiency Strategy

In recent years,the increasing environmental pollution and the development of the hydrogen-energy economy have driven national governments to pay attention to fuel cell technology,especially solid oxide fuel cells?SOFC?technology.The SOFC,as an electrochemical energy conversion device,has an more efficient conversion of chemical energy to electric energy in comparison with conventional power generation technology because it is not constricted by the carnot cycle.When the heat generated is used in cogeneration or gas turbine applications,further energy conversion efficiencies of 80%can be achieved.The development of high-efficiency and stable SOFC technology requires the use of excellent electrode materials.The La_0.3Sr_0.7Ti_0.3Fe_0.7O_3-??LSTF?perovskite constructed from iron and titanium is an attractive material due to its favourable catalytic performance.Because of high redox stability,La_0.3Sr_0.7Ti_0.3Fe_0.7O_3-??LSTF?perovskite oxide can be used as both anode and cathode materials for solid oxide fuel cells,it also has the advantage of low cost.In order to further improve the electrochemical performance of the LSTF perovskite,A-site deficiency of perovskite oxides was introduced as an effective way to enhance the oxygen ionic conductivity via extra oxygen vacancy generation.The expansion behavior and conductivity of the LSTF with A-site deficiency were characterized and analyzed in detail.In addition,electrochemical performance of the LSTF with the A-site deficiency were also explored as a symmetric electrode in the reversible mode.In this study,a series of(La_0.3Sr_0.7)_1-xTi_0.3Fe_0.7O_3-??LSTF-x,x=0?3%?5%?7%?9%?materials was prepared by sol-gel method.The effects of different A-site deficiency percentages on phase structure,microstructure,element valence,conductivity,thermal expansion and stability in redox atmosphere of LSTF were investigated,and electrochemical impedance spectroscopy?EIS?was tested.XRD results showed that the LSTF with A-site deficiency was partially decomposed in the hydrogen atmosphere,but the decomposition is reversible on certain conditions.This phenomenon suggested that the LSTF with A-site deficiency could be used as a symmetric electrode material.The EIS test showed that the material exhibited the lowest polarization resistance value in both air and hydrogen when the A site deficiency percentage was 5%.For instance,at 700^?,the impedance of LSTF-5%was 0.055 and 0.160?·cm² in air and hydrogen,respectively.It indicated that LSTF-5%possessed high electrocatalytic performance for both oxygen reduction reaction and hydrogen oxidation reaction.The full cell constructed with LSTF-5%as symmertric electrode,LSGM as electrolyte and LDC as barrier layer had the maximum power density of 602.7,431.8,289.3,163.5and 74.7 mW/cm² in SOFC mode at 850,800,750,700,650 ^?,respectively,which were much smaller than the full cell with LSTF symmetric eletrodes at the same temperature,indicating that a proper A site deficiency percentage can improve the electrocatalytic performance of the electrodes.When the full cell with LSTF-5%symmetric eletrodes was applied for high-temperature electrolysis of pure CO₂ in SOEC mode,under the condition of a polarization voltage of 1.3 V,the current density was 0.76 A/cm² at 800°C,and the polarization resistance was only 0.08?·cm².The long-term stability of CO₂ eletrolysis for 20h showed that the electrochemical performance performance was not greatly degraded,indicating that LSTF-5%was an excellent material for CO₂ eletrolysis.