Preparation And Properties Of Composite Cathode Materials For Proton Conductor Based Solid Oxide Fuel Cells

Energy and environmental issues are the main problems for today's social development,so to develop new clean and environmental friendly energy sources becomes an inevitable choice to realize the sustainable development of human beings.Solid oxide fuel cell(SOFC),as an energy conversion device which directly converts chemical energy into electric energy,with the advantages of high energy conversion efficiency,light environmental pollution and strong fuel adaptability,has become one of research hotspots.Traditional SOFCs require high operating temperature,which will bring the electrode sintering degradation,interface diffusion reaction and difficulty in sealing and other issues.So to lower the operating temperature of the battery has become the main research direction of SOFC.The proton conductor based solid oxide fuel cell(H-SOFC)has a low activation energy,which is an important way to realize the low operating temperature of SOFC.This paper mainly studies the electrochemical behaviors of batteries with different electrolytes and different components of cathode materials,and the influence of different cathode materials to the properties of the whole battery.In chapter 1,the research background,structure type,working principle,key material and conduction mechanism of SOFC are briefly introduced,and the development of H-SOFC and the main research contents of this paper are introduced.In chapter 2,the drugs and instruments used in the experiment are presented,and the methods of characterization and testing in the study are introduced.In chapter 3,a single cell of NiO-BaZr0.1Ce0.7Y0.2O3-?(NiO-BZCY)/ Ba Zr0.1Ce0.7Y0.2O3-?(BZCY)/ Ba0.5Sr0.5FeO3-?(BSF)-Ce0.8Sm0.2O2-?(SDC)was prepared.The initial powder was prepared by citrate combustion method.The structure of the powder was analyzed by XRD,and it was found that the initial powders were all well formed and no obvious impurity phases were produced.The power test for the single cell shows that the maximum power density(MPD)of the single cell at 750 ? is 413.5 mW·cm-2 and the open circuit voltage(OCV)is 0.926 V.The electrochemical impedance spectroscopy of the single cell shows that the cell has a small polarization resistance(Rp)at 750 ? as 0.301 ? cm2.The microstructure of the single cell cross section was investigated by scanning electron microscopy(SEM),and the effect of the microstructure on the battery performance was further studiedIn chapter 4,The H-SOFC were perpared with different cathode materials of Ba0.5Sr0.5FeO3-?(BSF)-Ce0.8Sm0.2O2-?(SDC)(7: 3,5: 5,3: 7 wt%)and the electrolyte of Ba Zr0.1Ce0.7Y0.1Yb0.1O3-?(BZCYYb).The effects of cathode components on the performance of the battery were studied.XRD results show that the BZCYYb powder exhibits a single perovskite structure,and the phase structure between the electrolyte BZCYYb and NiO is independent.The BSF and SDC are separated from the BSF-SDC composite powder after calcination.BSF shows cubic perovskite diffraction peaks,SDC has a fluorite structure,indicating that the chemical compatibility between BSF and SDC is good and could be used as composite cathode material.Thermal expansion analysis shows that the coefficients of thermal expansion of the three cathode materials at 200-750 ? is about 15.8 × 10-6 K-1,14.5 × 10-6 K-1 and 13.6 × 10-6 K-1,respectively.It is lower in thermal expension and more suitable for BZCYYb electrolyte compared with the cobalt based cathode.Electrochemical tests on three single cells show that the maximum power density and polarization resistance of BSF-SDC55 and BSF-SDC37 cells at 750 ? are 449 and 388 mW·cm-2,0.021 and 0.291 ? cm2,respectively.BSF-SDC73 cell is of better electrochemical performance,and the maximum power density(MPD)and the minimum interfacial polarization resistance(Rp)are 531 mW cm-2 and 0.019 ? cm2,respectively.The results show that BSF-SDC73 composite cathode may be a promising H-SOFC cathode material.The BZCYYb electrolyte exhibits better performance than BZCY.In chapter 5,the study in this paper are summarized,and the development of proton conductor based solid oxide fuel cell and its future work are prospected.