Performance Of Novel GdBaFe₂O_5+?-Based Doubleperovskite Electrode Materials For Solid Oxide Fuel Cells

Solid oxide fuel cell?SOFC?is a device that can directly convert chemical energy of fuel into electrical energy.It has the advantages of high energy conversion rate and low environmental pollution.More importantly,solid oxide fuel cells can directly convert the chemical energy in gaseous fuels,such as gas and natural gas,into electric energy,and the products are environmentally friendly.Therefore,SOFC,a new energy technology with high efficiency and cleanliness,has become one of the focuses of current research.In order to develop electrode materials with excellent electrochemical properties,an A site ordered layered oxygen deficiency double perovskite structure GdBaFe₂O_5+?symmetrical electrode material was studied.The electrochemical properties of the material were further improved by introducing Ba²⁺deficiency at A site.GBFO double perovskite structural material was synthesized by sol-gel method at 1000? in air and 1050? in hydrogen.The material is a tetragonal structure.The samples synthesized in different atmospheres have different oxygen vacancies,and the content of oxygen vacancies can be changed with the change of external environment.GBFO symmetrical electrode material has good chemical compatibility with LSGM and SDC electrolytes.TPD and TPR measurements show that the valence state of iron ions at B position of GBFO electrode material will change with the increase of temperature,thus introducing oxygen vacancy to improve the catalytic activity of the material.The average TEC values of GBFO samples in air and 5%H₂/Ar at 30-900? are 15.3×10^-66 K^–11 and 15.1×10^-6 K^–11 respectively?These values slightly higher than the thermal expansion coefficients of LSGM electrolyte materials.The thermal expansion matching between electrodes and electrolytes can be improved by introducing SDC buffer layer.SDC buffer layer as an excellent oxygen ion conductor,can increase the oxygen ion doping rate at the interface between electrodes and electrolytes.The conductivity of GBFO electrode materials in air is 3–10 S cm^–1,and that in H₂ is 4.1–24.4 S cm^–1,which is higher than many reported symmetric electrode materials.The results of electrochemical impedance measurements show that the polarization impedance of GBFO electrode material in air is better than many reported cathode materials.The LSGM electrolyte-supported single cells with GBFO as symmetrical electrode show high electrochemical performance when fueled with H₂,natural gas and CH₄.When fueled with synthetic gas containing H₂S,sulfur poisoning does not occur in the material.After 120 hours of continuous operation with CH₄ as fuel,no obvious performance degradation is found.Raman test results show that there is no carbon deposit on the surface of the material.It shows that GBFO has excellent carbon and sulfur resistance.GBFO is an excellent symmetrical electrode material for solid oxide fuel cells.GdBa_xFe₂O_5+??x=0.98?0.96?double perovskite structural material was synthesized by sol-gel method at 1050? in hydrogen.The material is a tetragonal structure.With the increase of A site Ba²⁺vacancy,the lattice volume shrinks and the oxygen vacancy concentration increases.When x=0.96,the material has the largest oxygen vacancy.GB_xFO anode materials have high conductivity in hydrogen.The conductivity of the materials can be improved by vacancy at A site.When x=0.98,the material has the highest conductivity.At 850?,the conductivity is 33.7 S cm^-1.It is higher than many reported anode materials.A site Ba²⁺vacancy hardly changes the thermal expansion coefficient of the material.Similarly,the thermal expansion matching between electrodes and electrolytes can be improved by introducing SDC buffer layer.The results of electrochemical impedance measurements show that the polarization impedance of GB_xFO anode material decreases gradually with the increase of the vacancy.When x=0.96,the material has the smallest polarization impedance.As far as the polarization impedance of 700? is concerned,the polarization impedance of GB_0.98FO anode material and GB_0.96FO anode material compared with the parent material GBFO decrease by 25.57%and 34.06%respectively.The single cells fabricated with GB_x FO as anode and LSGM as electrolyte have excellent electrochemical performance when H₂ is used as fuel.By introducing vacancies,the maximum power density of single cells are improved.When x=0.98,the single cell has the highest power density,and the maximum power density reaches 1052 mW cm^-2 at 850?.The results showed that the catalytic activity of the anode material is improved by introducing A site Ba²⁺vacancy.