| Fuel cells are the cutting-edge technologies that the national medium-and long-term science and technology development plan focuses on.Solid oxide fuel cells（SOFCs）operate at high temperatures and have high power generation efficiency（～40%-60%）,which has become the focus of research and development at home and abroad.At present,important factors hindering the practicality of SOFC technology are cost and stability issues caused by excessive operating temperatures.When the operating temperature is reduced to intermediate temperatures（800-600℃）,metal materials with better mechanical properties and low prices can be selected as support layer of SOFC,which can greatly reduce the production and operation costs of SOFC.However,when the temperature decreases,the oxygen reduction activity of the traditional LSM cathode becomes worse,the LSCF cathode has the problems of high cost and element segregation.In addition,the metal-supported single cell preparation technology is still immature.Therefore,it is of great significance to develop a low-cost,highly-reliable cathode and unit cell manufacturing method suitable for medium-temperature operation metal-supported SOFC（MS-SOFC）.In this subject,the perovskite oxide SrTi0.3Fe0.7O3-δwith excellent electrochemical performance was selected as the research object.The effects of doping Ni elements at the B-site and Sr2+deficiency at the A-site on the structure and electrochemical performance of the material were systematically studied.Developed a"reduction-reoxidation"method for constructing nano-microisomeric highly active cathodes,and realized the in situ construction of（Ni,Fe）xOy@STFN cathodes.And successfully used in metal-supported SOFC（MS-SOFC）cathode preparation.The results show that the cubic perovskite Sr1-xTi0.3Fe0.6Ni0.1O3-δ（x=0,0.02,0.05）series of oxides were successfully prepared at 1200℃ by solid-phase synthesis method.The introduction of A-site deficiency effectively reduces the thermal expansion coefficient of STFN cathode,increases the oxygen vacancy concentration,significantly reduces the cathode polarization impedance,and improves the output performance of the single cell.At 750℃ and an oxygen partial pressure of 0.21 atm,the polarization resistances of STFN-100 and STFN-95 are 0.135Ω·cm2 and 0.107Ω·cm2,respectively.In addition,the STFN-95 cathode has higher stability under lower oxygen partial pressure（0.14 atm）under simulated actual stack conditions.Anode-supported single cells operate stably for 400 hours under the conditions of 750℃ and 300m A/cm2 constant current discharge.Based on the above STFN-95 cathode,it was treated at 700-800℃ for 1h in a reducing atmosphere（3%H2O-5%H2/N2）,and then re-oxidized in 750℃ at air for 1 hour.（Ni,Fe）xOy@STFN nano cathode was constructed in situ.（Ni,Fe）xOy nanoparticles generated in-situ on the surface effectively promote the adsorption and dissociation of oxygen on the cathode surface,and significantly reduce the polarization resistance.The polarization resistance of the symmetrical cells after the reduction treatment at 750℃ was reduced from0.086Ω·cm2 to 0.044Ω·cm2 at 750 ℃ for p O2=0.21atm.In addition,the nano-modified cathodes exhibit better electrochemical catalytic activity for oxygen reduction reaction at low temperature and low oxygen partial pressure,and have practical value in SOFC reactors.Finally,metal oxide supported half-cells（Ni O-Fe2O3|Ni O-YSZ||YSZ）were prepared by co-casting and co-sintering processes.When the STFN-95 cathode is applied to metal-supported single cell,the maximum power density of the cell at 750℃ is 1.02W cm-2,and no performance degradation occurs during 100 hours of discharge.Finally,the single-cell“overall reduction method”was used to achieve the reduction of the support and the cathode in a 3%H2O-5%H2/N2 atmosphere.During the actual operation,fast temperature start-up and in-situ construction of a highly active nano-modified cathode were realized,and the maximum power density was 0.75W cm-2 at 750 ℃. |
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