Construction And Electrochemical Study Of Double Perovskite Cathode Material

Solid oxide fuel cells（SOFCs）have high energy conversion efficiency（up to 85%in the overall system efficiency）,environmentally friendly operation,and excellent fuel adaptability,arousing widespread attention in industry and academia.Aiming at the problems of oxygen transport kinetics,poor matching coefficient of thermal expansion,and poor resistance of carbon dioxide for the double perovskite cathode material at medium temperature,the lattice structure,and oxygen ion transport characteristics of the double perovskite-type cathode material are effectively regulated by elemental doping.And the reaction mechanism of the oxygen reduction process is studied further,and the electrochemical properties of the material are effectively improved.In addition,the optimized modified cathode material is also applied to the proton conductor SOFC,and the new vanadium nitride dehydrogenation catalyst is combined to achieve the cogeneration of electricity and ethylene.NdBaCo_2-xSc_xO_6-δ（x=0.00-0.25）series cathode materials are prepared by citric acid-EDTA sol-gel method,and the substitution by the low valence state Sc cause the reduction of the average valence state of Co elements in NdBaCo₂O_6-δ,and a large number of oxygen vacancies are introduced,which brought rapid oxygen surface exchange and bulk diffusion coefficients,thereby optimizing the oxygen ion transport characteristics.The polarization impedance of the NdBaCo_1.8Sc_0.2O_6-δcathode at 700 ℃ is 0.035Ω·cm²,which is 65%lower than that of the NdBaCo₂O_6-δcathode.Combined with the DRT analysis method and the polarization impedance analysis under different oxygen partial pressures,it can be seen that the rate-determining step of the NdBaCo_1.8Sc_0.2O_6-δcathode is the oxygen charge transfer process within the electrode/electrolyte interface.By doping the appropriate amount of large radius Zr element,the pure phase series NdBaCo_2-xZr_xO_6-δdouble-perovskite materials are successfully prepared,and a larger free volume of unit cells is obtained,and more oxygen vacancies are introduced into the unit cells,so that the structure optimization provided more transport channels for oxygen ions.The oxygen surface exchange and bulk diffusion coefficients of the cathode material at 700 ℃ reach 2.878×10^-4 cm·s^-1 and 5.827×10^-5 cm²·s^-1,respectively,and the polarization impedance value of the NdBaCo_1.95Zr_0.05O_6-δcathode at 700 ℃ is reduced to 0.024Ω·cm².The Zr doping improves Lewis acidity and hinders the adsorption of CO₂on the electrode surface,bringing a promoted CO₂ tolerance for the cathode.NdBaCo_1.95Zr_0.05O_6-δcathode has good chemical stability in the air with 5 vol.%CO₂,and after 50 hours of operation,the ASR increases slightly from the initial value of 0.030 to0.048Ω·cm² at a rate of 3.6×10^-4Ω·cm²·h^-1.In order to improve the thermal expansion compatibility of the double perovskite material and the electrolyte,the Fe-based NdBaFe_1.9Zr_0.1O_6-δcathode material was prepared.At 700 ℃,the k values of NdBaFe_1.9Zr_0.1O_6-δand NdBaFe₂O_6-δwere 1.61×10^-4and 1.28×10^-4 cm·s^-1,respectively,and the corresponding D values were 4.20×10^-5 and 2.72×10^-5 cm²·s^-1,respectively.The polarization resistance of NdBaFe_1.9Zr_0.1O_6-δin air at700 ℃ is 0.066Ω·cm²,which is lower than the 0.104Ω·cm² of the NdBaFe₂O_6-δcathode.After 54 hours of operation at 700 ℃,the polarization impedance of NdBaFe_1.9Zr_0.1O_6-δincreases only slightly from the initial 0.065Ω·cm² to 0.073Ω·cm².In addition,when hydrocarbons are used as fuels,the resulting CO₂ can exacerbate the greenhouse effect.In view of this problem,an anode-supported SOFC based on vanadium nitride,a new platinum-like ethane dehydrogenation electrocatalyst is designed and constructed,using a well-matched Fe-based NdBaFe_1.9Zr_0.1O_6-δcathode material,and a uniform and continuous VN catalyst layer are modified on the BZCYYb-Ni porous anode framework by impregnation process.The hydrocarbon fuel is directly electrochemically catalyzed for dehydrogenation,and the ethylene product is obtained at the same time as the power generation is obtained.Using the DFT calculations,the electrocatalytic reaction mechanism of this new transition metal nitride catalyst is understood and understood from the molecular level.The porous anode microstructure is optimized to achieve efficient cogeneration of electricity and ethylene,with a conversion rate of 29.7%for ethane,96%selectivity for ethylene,and a peak discharge power density of 101 mW·cm^-2 at 700 ℃.In addition,the SOFC produces high-value chemicals while producing electricity,this paper is based on the previous research work,using the optimized Fe-based NdBaFe_1.9Zr_0.1O_6-δcathode material,and prepared a"platinum-like"vanadium oxide dehydrogenation catalyst,using the impregnation process to modify the VN catalyst layer on the BZCYYb-Ni porous anode skeleton,design and construct proton conducting anode supported SOFC with configuration of NdBaFe_1.9Zr_0.1O_6-δ/BZCYYb/BZCYYb-Ni-VN.It directly electrochemically catalyzes the dehydrogenation of hydrocarbon fuels,and obtains ethylene products while producing electricity.At the same time,the porous anode microstructure was optimized and designed to achieve efficient cogeneration of electricity and ethylene,and the conversion rate of ethane is 29.7%,the selectivity of ethylene was 96%,and the peak power density is 101 mW·cm^-2.