Study On Modification And Electrochemical Stability Of LSCF Cathode Materials

The Environmental pollution caused by fossil fuel burning has become a huge obstacle to human survival and development,posing a huge challenge to the sustainable development of human life and social economy.Searching for efficient and clean renewable energy has become a hot topic in today’s society.Solid Oxide Fuel Cells（SOFCs）is an all-solid-state efficient device that can convert chemical energy into electrical energy.Due to its environmental friendliness and high Fuel efficiency,SOFCs has become one of the effective ways to solve these problems.La_0.6Sr_0.4Co_0.2Fe_0.8O_3-σ（LSCF）cathode material is considered as the most potential cathode material at intermediate temperature due to its high conductivity and oxygen catalytic activity at intermediate temperature and matching with the thermal expansion coefficient of electrolyte LSGM and SDC at medium temperature.However,the electrochemical stability of solid oxide fuel cell（SOFC）is decreased due to the phenomenon of Sr O segregation on the electrode surface of LSCF cathode material under long-term working conditions.At the same time,with the application of metal connectors in SOFC,the volatile Cr O3 gas on the metal surface will react with the surface Sr O to generate Sr Cr O3 insulating phase,which further degrades the catalytic activity of LSCF cathode material and impedes the application of LSCF cathode material in IT-SOFC.In this paper,taking La_0.6Sr_0.4Co_0.2Fe_0.8O_3-σperovskite cathode material as the research object,LS（CF）_1-xSc_x（x=0.025、0.050、0.075、0.100）series cathode material and impregnated nitrate solution were designed and synthesized to prepare surface modified LSCF cathode material.The structure,properties and stability of LSCF cathode materials modified by two different methods were studied in detail.The results show that Sc³⁺cannot participate in the charge transfer process in the oxygen reduction reaction due to its stable valence,which reduces the conductivity of LSCFSc cathode material after doping Sc³⁺.The second phase La Sr Fe O₄is generated when the doping amount is≥0.075mol,which further reduces the conductivity of the cathode material.As the doping amount of Sc³⁺increases,the polarization surface resistance of the cathode material decreases significantly.The polarization surface resistance ASR of LSCFSc_0.075cathode material at 800℃is only 0.05Ωcm².The maximum power density of the anode supported single cell using LSCF as the cathode material is 542.7 m W/cm²at 750℃,while the power density of the anode supported single cell using LSCFSc_0.075as the cathode material is increased to 861 m W/cm².Compared with the single battery with LSCF as cathode material,the maximum power density improved by 58.7%.In order to further study the stability of LSCFSc cathode materials,the thermal stability and Cr toxification resistance of LSCFSc series cathode materials were investigated at 750℃.The results show that LSCFSc_0.050has the best thermal stability after 7200 min of continuous operation,and the polarization surface resistance ASR increases from 0.24Ωcm²to 0.30Ωcm².Under the same conditions,the polarization surface resistance ASR of LSCF increases from the initial 0.40Ωcm²to 0.66Ωcm².After7200 min of Cr toxicity,LSCFSc_0.050also showed the best Cr toxicity resistance,and the polarization surface resistance ASR increased from the initial 0.23Ωcm²to 0.49Ωcm².Under the same conditions,the polarization surface resistance ASR of LSCF increases from the initial 0.51Ωcm²to 1.16Ωcm²,indicating that a small amount of Sc doping improves the anti-Cr toxicity stability of LSCF cathode material.It is found that surface impregnation can improve the catalytic activity of the cathode material and inhibit the deposition of Cr vapor on the cathode surface.La Ni_0.6Fe_0.4O₃（LNF）is an excellent cathode material resistant to Cr poisoning,and has similar crystal structure to LSCF cathode material.It can impregnate nitrate solution of LNF on the surface of LSCF cathode by impregnation method and prepare nanoparticles in situ to reduce the interface resistance.In this study,different impregnation amounts of surface modified LSCF cathode materials were synthesized.The results showed that the impregnation solution formed a new phase of hexagonal perovskite structure on the surface of LSCF.The ASR of 8%wt and 12%wt surface modified LSCF cathode materials at 800℃is 0.08Ωcm²and 0.09Ωcm²,respectively.The power density of anode-supported single cell prepared by surface modified LSCF cathode material with impregnation amount of 8%wt was increased to 698.1 m W/cm²,and the maximum power density was 28.6%higher than that of the single cell without surface modification.The results show that surface modification can improve the electrochemical stability of LSCF cathode materials.After continuous operation at 800℃for 7200 min,the surface modified LSCF cathode material with impregnation amount of 12%wt showed the best thermal stability,and the polarization surface resistance ASR increased from the initial0.08Ωcm²to 0.11Ωcm².Under the same conditions,the polarization surface resistance ASR of LSCF increases from the initial 0.40Ωcm²to 0.66Ωcm².After Cr poisoning at800℃for 7200 min,LSCF@12%wt LSNCF also showed the best resistance to Cr toxicity,and the polarization surface resistance ASR increased from 0.12Ωcm²to 0.18Ωcm².Under the same conditions,the polarization surface resistance ASR of LSCF increases from the initial 0.25Ωcm²to 2.17Ωcm².