Study On Electrochemical Performance And Stability Of La_xSr_1-xTiO₃ Nanofiber-based Composite Anodes

Nowadays,the rapid developments of science,technology and economy are restricted by energy crisis and environmental pollution.Solid oxide fuel cell（SOFC）is an new type of energy conversion device that can convert chemical energy directly into electrical energy,and it has attracted an increasing attention due to their high efficiency,fuel universality and low pollution.Conventional Ni-based anodes have lots of disadvantages,and developing alternative anodes with long life and excellent performance is imperative.We determined the optimum process parameters for electrospinning to prepared the pure perovskite structure La_xSr_1-xTiO₃（x=0.2,0.3,0.4）nanofibers with smooth surface and relatively uniform diameter and length.Based on the electrochemical reaction triple-phase boundary theory,the composition and the microscopic morphology of La_xSr_1-x-x TiO₃ scaffolds and the composition of Gd_yCe_1-y-y O_2-δ（y=0,0.1,0.2,0.3）impregnation phase were investigated to find the influence of them on the anodes electrochemical performances.As the increase of La doping ratio（0.2≤x≤0.4）,the electrochemical performance of the La_xSr_1-xTiO₃ anodes improved,and the optimal La doping ratio of the La_xSr_1-x-x TiO₃ scaffolds had been found to be 0.4.The Gd_yCe_1-yO_2-δimpregnation phase was added into the La_xSr_1-xTiO₃ anode by ion impregnation.As the increase of Gd doping ratio of Gd_y Ce_1-yO_2-δphase,the electrochemical performance improved firstly and then degraded,and the optimal Gd doping ratio of the Gd_yCe_1-y-y O_2-δimpregnation phase had been found to be 0.2.The experiments show that the nanofiber-based La_xSr_1-xTiO₃ scaffolds had higher capacity for the Gd_yCe_1-yO_2-δimpregnation phase.Based on the researches of the anode scaffolds and the impregnation phase,in order to improve the electrochemical performance of the La_xSr_1-x-x TiO₃-based composite anodes fueled with methane,nanofiber-based La_0.4Sr_0.6TO₃（LST）-Gd_0.2Ce_0.8O_1.9（GDC）-Ni composite anodes were prepared by ion impregnation technology.At 900°C,the polarization resistance was 0.68Ω·cm² and the maximum power density was 83.0mW·cm^-22 for the LST-GDC-Ni（LST:GDC:Ni O=1:1:0.1）composite anode when fueled with humid CH₄.When the mass ratio of Ni did not exceed 40 mass%（NiO:LST）,the electrochemical performance of the nanofiber-based LST-GDC-Ni composite anodes improved slightly after working at humid CH₄ atmosphere for a long time,and the composite anodesshowed excellentresistancetocarbondepositing.The electrochemical performance of the single cells did not degrade significantly after 30 thermal cycles（900°C⁷00°C）for 2700 min or 10 redox cycles for 240 h,and the nanofiber-based LST-GDC-Ni composite anodes showed excellent thermal cycling stability and redox cycling stability.The electrochemical performance degraded significantly after fueling with 512 ppm H₂S-H₂ for 21 h,the LST-GDC-Ni composite anode showed a poor resistance to sulfur poisoning.In order to improve the sulfur poisoning resistance of the composite anodes,we prepared the nickle-free nanofiber-based LST-GDC-Co composite anodes by ion impregnation technology.The polarization resistances of the LST-GDC-Co（LST:GDC:NiO=1:1:0.3）after reducing were 0.48Ωcm² and 1.97Ωcm² when fueled with humid H₂ and CH₄ respectively,which were lower than those of the LST-GDC-Ni（LST:GDC:NiO=1:1:0.3）composite anodes,and the LST-GDC-Co composite anode showed good electrochemical performance.After sulfur poisoning for 24 h,the electrochemical performance changed worsen slightly but far better than the LST-GDC composite anodes without infiltrating Co.The LST-GDC-Co composite anode showed a strong resistance to sulfur poisoning.The polarization resistances and the maximum power densities the LST-GDC-Co composite anode after sulfur poisoning did not change significantly after carbon depositing for 100 h,and the LST-GDC-Co composite anode after sulfur poisoning showed an excellent resistance to carbon depositing.