The Design And Electrochemical Properties Of Perovskite-like Cobalt-based Solid Oxide Fuel Cell Cathode Materials

Medium-temperature solid oxide fuel cells?SOFC?have attracted extensive attention due to their pollution-free and high-efficiency energy conversion.As the main component of the solid oxide fuel cell,the cathode material has always been the focus of research.In this paper,the perovskite-like oxide PrSrCoO_4±?is used as the research object to optimize the design from the perspectives of B-site doping with different transition metals and A-site defect design,and the characterization of its physical and chemical properties and electrochemical properties are studied in detail.The main research contents are as follows:1.The cathode materials of PrSrCo_1-xCu_xO_4+??x=0.0,0.1,0.2,0.3,0.4,0.5?are synthesized by traditional solid state reaction method.The phase and chemical stability of the materials are tested by XRD.The results show that all the products are crystlized in single-phase K₂NiF₄ structure,and the space group is I4/mmm.Cathode materials and electrolyte Ce_0.9Gd_0.1O_1.95?CGO?has good chemical stability at 1000?.Within the temperature range of 100-800?,the cathode materials exhibit good thermal expansion compatibility with CGO electrolyte.The doping of Cu increased the conductivity of these materials.The conductivities of PrSrCo_0.7Cu_0.3O_4+?exceed 206.8 S cm^-1 in the intermediate temperature range of 100?800 ^oC.PrSrCo_1-xCu_xO_4±?system exhibited excellent performance.When the doping content of Cu is 30%,the electrodegive the lowest polarization resistance?0.08?.cm²?at 700 ^oC in air.The results of cathodic reaction mechanism show that the rate limiting step of oxygen reduction reaction?ORR?on the electrode is oxygen dissociation,adsorption and diffusion process.The output of a single cell made of PrSrCo_0.7Cu_0.3O_4+?and CGO is 296.5 mW cm^-2 at 700?with wet hydrogen as reducing agent and air as oxidant.2.The PrSrCo_1-xNi_xO_4+??x=0.0,0.1,0.2,0.3,0.4,0.5?cathode materials are synthesized by solid state reaction method.The phase,high temperature chemical compatibility,thermal expansion coefficient,electrical conductivity and cathodic electrochemical properties of the material are characterized and tested.The results show that the PrSrCo_1-xNi_xO_4+?series materials are all crystallized into single-phase K₂NiF₄structure,the space group is I4/mmm and has good high temperature chemical compatibility and thermal expansion matching with electrolyte CGO.As the doping concentration of Ni ions increases,the conductivity of the material increases first and then decreases,and the highest conductivity at 800°C is reached.186 S cm^-1.The results of cathode polarization resistance study show that the area polarization resistance of PrSrCo_0.7Ni_0.3O_4+?reach the minimum value of 0.14?·cm² at 700°C in air.Further investigation of the oxygen reduction reaction?ORR?reaction rate limiting step results show that the material ORR reaction rate limiting step is the oxygen dissociation,adsorption and diffusion process.The output of a single cell made of PrSrCo_0.7Ni_0.3O_4+?and CGO is 215.8 mW cm^2-at 700?with wet hydrogen as reducing agent and air as oxidant.3.The Pr_1-xSrCo_0.5Ni_0.5O₄₊?(P_1-xSCN,x=0.0,0.05,0.10,0.15)series of cathode materials are synthesized by traditional solid state reaction method.The phase,thermal expansion coefficient?TEC?,conductivity,electrode morphology and electrochemical properties are characterized.XRD results show that the oxides crystallize in a single K₂NiF₄ structure with a space group of I4/mmm.The cathode materials exhibited good high temperature chemical compatibility with electrolyte Ce_0.9Gd_0.1O_1.95?CGO?.Iodometry analysis shows that with the increase of Pr³⁺vacancy concentration,the average valence of Co/Ni ions in oxides increased stepwise with the increase of x and then decreased after x=0.10,while the content of oxygen vacancy increased gradually.Introducing Pr³⁺vacancy significantly improved the conductivity of the material.The highest conductivity of 309 S·cm^-1 was found in P_0.90SCN at 700?in air.The thermal expansion measurement results show that TEC increased with the increase of Pr³⁺deficiency,and the maximum value is 1.51×10^-5 K^-1.Electrochemical impedance spectroscopy?EIS?measurements show that Pr vacancy significantly reduced the polarization resistance of the electrode,and the smallest polarization resistance of 0.21?·cm² was obtained on P_0.90SCN cathode at 700?in air.The maximum output power density of electrolyte supported single cell NiO-CGO/CGO/P_0.90SCN was 197.8mW·cm^-2 at 700?...