Study On Preparation And Performance Of BaFeO_3-δ-Based Electrodes For Solid Oxide Fuel Cells

Solid Oxide Fuel Cell（SOFC）is an all-solid-state electrochemical power generation device that directly converts chemical energy stored in Fuel into electric energy efficiently and environmentally friendly.It plays an important role in green and low-carbon energy transformation and is a promising energy conversion storage and carbon neutralization technology in the future.SOFC electrode is the site of fuel oxidation reaction（anode）and oxygen reduction reaction（cathode）,the properties and performance of the electrode is the key factor to determine the stability of SOFC high power output,the design and development of new electrode materials and electrode reaction process research has been a hot spot in the field of SOFC.Cubic BaFeO_3-δperovskite is a potential SOFC electrode material with high oxygen ionic conductivity and good catalytic activity for oxygen reduction.In this paper,a novel BaFeO_3-δelectrode is optimized by doping strategy,and the properties and properties of the electrode are systematically studied.The main contents of this thesis are as follows:Ba Zr_0.1Fe_0.9-xNi_xO_3-δ（x=0.1,0.15,0.2,0.25）nano-powders were synthesized by citric acid-nitrate combustion method.The effect of Ni doping on the phase structure was revealed.When doping amount x=0.15,0.2,the powders were cubic perovskite structure that has disordered oxygen vacancy distribution and isotropy crystallographic symmetry,which is beneficial to oxygen ion and electron transport process.Therefore,Ba Zr_0.1Fe_0.75Ni_0.15O_3-δ（BZFN15）and Ba Zr_0.1Fe_0.7Ni_0.2O_3-δ（BZFN20）were selected as the research objects to systematically study their properties as the cathode of proton-conducting SOFC.XPS results showed that Feand Ni are mixed valence states of Fe^3+/4+and Ni^2+/3+,respectively.TG and titration tests showed that the oxygen vacancy concentration of BZFN15 material was higher,which was conducive to the catalytic reduction of oxygen.BZFN15 exhibits higher conductivity in humid air,with a maximum conductivity of 8.69 S cm^-1.BZFN15 has larger D_chem and k_chem values of 2.32×10^-5 cm²s^-1 and 1.40×10^-3 cm² s^-1,respectively,which means rapid oxygen molecular division and oxygen ions entering the cathode layer.BZFN15 and BZFN20 cathodes maintain good chemical compatibility with BZCY electrolyte under SOFC single cell preparation and operation conditions,but their thermal expansion coefficient is twice that of BZCY electrolyte.As its thermal expansion coefficient is twice that of BZCY electrolyte,considering the bonding strength and thermal cycling stability of cathode|electrolyte interface,the composite cathode is constructed with BZCY to carry out the study on electrode process of symmetrical cells and electrochemical performance of single cells.The results show that the main rate control steps of the electrode are oxygen adsorption dissociation and reduction reaction steps.The maximum power density of the single cell is 583 m W cm^-2 at 700 ^oC,and the polarization resistance is 0.087Ωcm² under open circuit condition.BaFe_0.8Ce_0.1Nb_0.1O_3-δ（BFCN）cubic perovskite nano-powders was prepared by solid state reaction method in order to develop a CO₂-resistant cathode with low temperature and high performance.Compared with BaFe_0.9Ce_0.1O_3-δ（BFC）,it is found that Nb improves the resistance to CO₂ and reduces the thermal expansion coefficient of the material.The average TEC value decreased from 23.01×10^-6 K^-1 to 20.88×10^-6 K^-1 due to Nb doping,which will improve the interface contact between cathode and electrolyte.The characterization and analysis of the polarization resistance of symmetric cells under the condition of 10%CO₂ show that Nb substitution at Fesite can optimize the degradation of oxygen adsorption dissociation and charge transfer performance caused by CO₂,weaken the alkalinity and strengthen the average metal oxygen bond,and inhibit the CO₂ adsorption and formation of insulating carbonate.The anode-supported single cell with the BFCN-SDC composite cathode has a high power density of 680 m W cm^-2and a low polarization resistance of 0.119Ωcm² at 700 ^oC.In conclusion,this work provides a candidate for IT-SOFC cathode materials with outstanding resistance to CO₂.The symmetrical electrode material Ba_0.7La_0.3Fe_0.9Nb_0.1O_3-δ（BLFN）was designed and its related properties and electrochemical properties were studied.BLFN material shows excellent structural stability in wet H₂ reducing atmosphere and good chemical compatibility with La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ（LSGM）electrolyte,which meet the requirements of symmetrical solid oxide fuel cell（SSOFC）electrodes.The BLFN-SDC composite electrode was constructed by adding SDC to optimize the electrochemical performance of THE BLFN electrode.It was found that the addition of SDC had an obvious optimization effect on the charge transfer process in the electrode polarization reaction.The optimal ratio of BLFN to SDC was 7:3（BLFN-SDC73）.At 800 ^oC,the single cell with BLFN-SDC73 symmetrical electrode and LSGM electrolyte has a peak power density of 737 m W cm^-2 and a polarization resistance of 0.077Ωcm².SSOFC showed good stability in 10 cycle stability tests and 100 hours of long-term performance tests,indicating that BLFN-SDC73 is a promising SSOFC electrode material.