Investigation On Property And Performance Of Materials For Intermediate Temperature Solid Oxide Fuel Cell

Solid oxide fuel cell(SOFC)converts the chemical energy of fuel directly into electricity via electrochemical pathways with a high energy efficiency and low environment impacts.The high operating temperature(800 oC and above)leads to many benefits,but also causes a lot of serious problems.Working at intermediate temperature(IT)range of 400 to 800 oC is the main trend of SOFCs.The optimization and development of fuel cell's material,structure as well as fabricating process,to realize the direct utilization of non-hydrogen fuels,is the key point of IT-SOFC development.To this end,some attempts and progresses of this thesis are as follows:(1)In Chapter 2,Sr2Fe1.5Mo0.5O6-?(SFM)perovskite material prepared as IT-SOFC anode,shows good performance of the direct utilization of non-hydrogen fuels,as well as a good coking resistance.SFM material is prepared via a combined citrate-EDTA complexing method,and it can be stable in both oxidizing and reducing atmosphere.By using SFM as anode,a single cell with the electrolyte support configuration of SFM|La0.8Sr0.2Ga0.83Mg0.17O3-?|Ba0.5Sr0.5Co0.8Fe0.2O3-? is fabricated by screen-printing method.When using methanol or ethanol as fuel,the cell exhibits a maximum power density of 431 and 340 mW cm-2 at 800 oC,respectively.And no cooking formation is observed on the SFM anode.(2)In Chapter 3,a novel single layer fuel cell(SLFC)is successfully fabricated based on Ce0.8Sm0.2O2-?-Na2CO3 and SFM composite material.The relation between SLFC's electronic and ionic conductivity ratio and its performance is revealed.The SFM content in composite material shows a great influence on the open circuit voltage(OCV)and the output of the SLFC.The single cell made of 30 wt.% SFM exhibits the highest OCV of 1.05 V and output of 360 mW cm-1 at 750 oC,which is comparable to the conventional three-layer fuel cell.By discussing the influence factors of the single cell's OCV,it is further revealed the relationship of the electronic and ionic conductivity ratio with the OCV and output of SLFC.(3)In Chapter 4,the property and performance of LiNi0.5Mn1.5O4(LNM)spinel to be used as IT-SOFC cathode is investigated,and the relation between the electrode performance and the oxygen uptake and release ability of LNM is elaborated.LNM material shows good thermal stability and compatibility with YSZ electrolyte,as well as a conductivity of 5 S cm-1 at 800 oC in air.The high content of Mn4+ favors oxygen activation and provides better oxygen exchange kinetics,which lead to the better electrode performance of LNM cathode than the traditional La0.8Sr0.2MnO3 cathode at temperature above 700 oC,and the faster oxygen uptake and release behavior as well as the larger movable oxygen amount based on TG results.(4)In Chapter 5,a novel method of 4-probe EIS measurement is brought up to investigate IT-SOFC electrolyte materials.The EIS curves and DC resistances of both 4-probe and 2-probe methods are measured on conventional Gd0.1Ce0.9O2(GDC)material.According to the results of above measurements,the EIS fitting analysis as well as the resistance origin verification experiments,4-probe EIS method could get the impedances of material without the influence of interfacial processes on electrodes,which provides better understanding of interfacial steps in the material.In addition,this 4-probe EIS method could be further used to study the more complex doped ceria-carbonate composite electrolyte system.Corresponding work is still undergoing.