Preparation And Performance Study Of Ceramic Anode Materials For Solid Oxide Fuel Cells

Solid oxide fuel cell?SOFC?is a power generation device that directly converts the chemical energy of fuel into electrical energy.Compared to other kinds of fuel cells,SOFC has the advantage of fuel flexibility,which allows not only hydrogen but also hydrocarbon as fuel gas.However,the taditional N i-based anodes have poor resistance to carbon deposition,sulfur poisoning and particle coarsening,leading to the performance deactivation.Recently,the ceramic anodes with the mixed electronic-ionic conductivity gradually become one of the research hotspot due to their excellent resistance to carbon deposition and sulfur poisoning.In this thesis,the important work is focused on the development and opertimization of W-doped SrFe O_3-?ceramic anode.In C hapter 1,the working principle,cell configuration,key materials?specially anode materials?of SOFC were reviewed.In addition,the anode optimization methods and EIS-DRT?Electrochemical impedance spectra-Distribution of relaxation times?analysis method were introduced.Aiming at the challenge of SOFC anode materials,the research goal and important content of this thesis were put forward.Chapter 2 briefly introduces the main preparation process including ceramic powder,single SOFC and some other testing samples.The chemical reagents,measurement equipments and characterization methods used in this thesis were listed.In C hapter 3,SrFe_0.8W_0.2O_3-??SFW?perovskite oxide was prepared by a modified citrate-EDTA-nitrate combustion method and explored as an electrode material for symmetrical solid oxide fuel cell?SSOFC?.It is found that tungsten dopant can stabilize the cubic perovskite structure of SrFe O₃ and increases the resistance to reducing atmosphere,demonstrating its great potential as an alternative SOFC anode.Meanwhile,the catalytic activity of SFW as SSOFC electrode has been deeply studied.At 800?,the area specific polarization resistances?ASRs?of SFW|La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-??LSGM?|SFW SSOFC are measured to be as low as 0.084and 0.20?cm² in air and H₂,respectively.EIS-DRT analysis of SFW electrode processes at different hydrogen partial pressures,oxygen partial pressures and testing temperatures reveals that the rate-limiting step in anode conditions is associated with hydrogen adsorption/dissociation process at SFW surface and while in cathodic conditions is ascribed to the dissociation of adsorbed oxygen and charge transfer processes.LSGM electrolyte-supported SSOFC with SFW electrode exhibits a high power density of 930 m W cm^-2 and low polarization resistance of 0.075?cm² at 850? when using hydrogen as fuel gas and air as oxidant,indicating that SFW is a promising SSOFC electrode material.In Chapter 4,novel SrFe_0.75W_0.2Ni_0.05O_3-??SFWN?anode was prepared to optimize SFW anode.SFWN can be partially reduced under wet hydrogen at 800 ?,and as a result,N i Fe-alloy nanoparticles in-situ form on the surface of SFWN perovskite parent.Surface decoration of N i Fe alloy nanoparticles improves the hydrogen oxidation reaction?HOR?kinetics at anode and decreases ASR values from0.2?cm²for SFW to 0.125?cm² for SFWN at 800 ?.EIS-DRT analysis reveals that the rate-limiting step of SFWN anode process is still hydrogen adsorption/dissociation process.In contrast with SFW anode,the surface decoration significantly accelerates the hydrogen adsorption and disassociation process.When the humidified hydrogen was used as fuel gas and ambient air as oxidant,the peak power densities of La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-??LSGM?-supported SOFC with SFMN anode reach 330,573,and 769 m W cm^-2 at 700,750,and 800°C.The durability for 100 hours indicates that the essentially complete exsolution process can be achieved during 40 hours and then SFMN anode keeps excellent performance stability.These results suggested that SFWN material is a potential good candidate as a high-performance ceramic anode for SOFC.In Chapter 5,W-doped Sr Co O_3-?materials were studied to use as SOFC cathode materials.The solid solubility of W in Sr Co O_3-?is low,and Sr₃Co₂WO₉ impure phase appears when the doping content reaches at 0.1.In 200-800 ? temperature range,the electrical conductivities of W-doped Sr Co O_3-?materials exhibit the semiconductor behavior.The electrical conductivities of Sr Co_0.9W_0.1O_3-?and Sr Co_0.85W_0.15O_3-?are lower than Sr Co_0.95W_0.05O_3-?due to the appearance of impure phase.SCW0.05|Sm_0.2Ce_0.8O_2-??SDC?|SCW0.05 symmetrical cell shows low ASR values in air,0.13?cm² at 700 ?.The peak power densities of anode supported 650 ?,428.9 m W cm^-2at 600 ? and 281.4 m W cm^-2at 550 ?,respectively.