【作者】 于洁；

【导师】 王华；

【作者基本信息】 昆明理工大学 ， 材料学， 2009， 博士

【摘要】 中温(500℃-850℃)条件下如何提高固体氧化物燃料电池(SOFC)电极材料的性能,是中温固体氧化物燃料电池(ITSOFC)开发的关键问题之一。为了获得优良的ITOFC阴极材料,本文中对掺杂的钙钛矿型复合氧化物材料La1-xAxM1-yNyO3-δ(A为Sr, Ca等；M和N为Fe, Mn, Co, Cu等)进行了合成、结构表征和性能研究,对材料合成工艺进行了优化,探索了不同组成材料体系的结构与性能之间的关系。采用了EDTA螯合溶胶-凝胶法和甘氨酸-硝酸盐法(GNP)合成了La1-xSrxCo1-yFeyO3-δ(LSCF)、La0.8Sr0.2Co0.085CuxFe0.915-xO3-δ(LSCCuF)、La0.8Sr0.2Co0.05FexMn0.95-xO3-δ(LSCF)和La0.8Sr0.04Ca0.16Fe1-zCozO3-δ(LSCaCF)等材料体系。通过差热-热重分析(TG-DTA)、X射线衍射分析(XRD)、扫描电镜-能谱分析(SEM-EDS)、透射电子显微镜(TEM)、氮吸附仪(BET)和激光粒度分析等手段研究了合成过程和材料的结构特征。用碘滴定法测定了合成材料的非化学计量氧值；利用光电子能谱技术(XPS)分析了掺杂后元素的价态。采用TG-DTA、SEM及XRD技术研究了材料的热、化学相对稳定性；采用氧程序升温脱附(O2-TPD)和催化反应装置来研究材料的氧化还原催化活性；采用直流四探针法和电化学阻抗谱测定了材料的电导性能。研究得到EDTA螯合溶胶-凝胶法合成LSCF材料的优化工艺条件为：溶液的pH值控制在中性到碱性范围内；对有机试剂量进行选择时,合适的比例是金属离子与EDTA螯合剂的摩尔比在1：1.1-1：1.2之间,乙二醇与EDTA螯合剂的摩尔比为3：1；脱水温度在60℃-70℃之间；焙烧温度在700℃-800℃之间。采用该优化工艺合成的LSCF材料为钙钛矿结构。随着Sr掺杂量x的增加,晶胞向尺寸减小的方向畸变。合成粉末为近似球形颗粒,比表面积为11.6m2/g,平均孔容量0.034cc/g,平均孔径11.9nm。材料二次颗粒平均粒度约0.18μm,分布比较均匀。材料中存在不同的氧物种：表面弱吸附氧、氧空位吸附氧和晶格氧。A位Sr的掺杂使得表面吸附氧量增加,而B位元素对氧物种的影响较小；A、B双掺杂的材料比单掺杂的材料La3d5/2和O1s结合能都有所降低,说明化合物中存在着离域d电子,材料的导电性好。A位和B位的掺杂促进了高价离子的生成。材料的混合电导率在所测温度范围内(200℃-850℃)随温度升高而增大,呈现类似半导体的导电特性；所制备的材料电子电导率高,有一定的离子电导。材料与钙钛矿型氧化物电解质La1-xSrxGa1-yMgyO3-δ(LSGM)化学相容性好。对EDTA螯合溶胶-凝胶法和甘氨酸-硝酸盐法(GNP)两种工艺的特点进行了比较：两者均可得到纯钙钛矿相复合氧化物粉末,但粉末形貌显著不同；EDTA螯合溶胶-凝胶法合成粉末粒度小而均匀,粉末颗粒分散性好,但所需合成时间较长；甘氨酸-硝酸盐法合成粉末的优势在于合成时间大大缩短,合成粉末孔隙度高,比表面大,有利于阴极材料的氧传输。采用甘氨酸-硝酸盐法(GNP)制备了在B位上同时掺杂两种元素的(LSCCuF)和(LSCFM)阴极材料。元素组成为(LSCCuF-0.3)时得到无杂相的钙钛矿型复合氧化物结构,材料的实际组成与设计组分相符。采用直流四探针法测量了LSCCuF系列材料的电导率,得到其电导率随Cu含量的增加先增大后减小；LSCCuF-0.3的电导率随温度的增加先增大后减小,在600℃达到最大值(1809.47S/cm),LSCCuF-0.3在空气气氛中的电导率大于在氩气气氛中的电导率。LSCCuF-0.3与LSGM化学相容性较好。合成的LSCFM系列材料为单一的钙钛矿相,没有其他杂质相的存在。该系列材料的氧非化学计量值(δ)随x的增大而减小。该材料制备的膜片用扫描电镜(SEM)和能谱仪(EDS)进行形貌观察和元素分析,结果表明制备的材料致密度高,组成符合设计组分,无杂质元素。材料的电导率随着温度的升高而增大,同时随着x的增大而减小,其中x=0的电导率最大,在850℃时达到了64.54S·cm-1。采用甘氨酸-硝酸盐法(GNP)合成了A位上同时掺杂两种元素的La0.8Sr0.04Ca0.16Fe1-zCOzO3-δ(LSCaFC)材料,为钙钛矿型复合氧化物结构,材料的组成成分与设计相符。得到的粉末比表面积大,粒度小,有团聚现象。随着Co/Fe比例的增加,材料的氧非化学计量值δ增加,氧空位浓度增加；Sr和Ca的同时掺杂能促进氧空位的生成。LSCaFC材料的电导率随温度升高而增大,其中La0.8Sr0.04Ca0.16Fe0.4Co0.6O3-δ材料电导率较高,从550℃到850℃的电导率均大于100S/cm,可以满足中温固体氧化物燃料电池阴极材料的电导率要求。LSCaFC材料与LSGM电解质的化学相容性好。采用合成的阴极材料及课题组制备的电解质和阳极材料,用丝网印刷-共烧结成膜技术、旋涂-共烧结成膜技术制作平板式SOFC单电池,并进行性能考察。以H2(0.5L/min)为燃料,空气(0.5L/min)为氧化剂,以La1-xSrxCr1-yMnyO3.δ(LSCrM)为阳极,La1-xSrxGa1-yMgyO3.δ(LSGM)为电解质,LSCF掺杂50% LSCrM材料为阴极的LSCrM| LSGM| LSCF (LSCrM50%)单电池在850℃时的开路电压为0.998V,最大功率密度为97mW/cm2;以H2(0.1L/min)为燃料,空气(0.14L/min)为氧化剂,650℃时,以La1-xSrxCr1-y-zMnyCozO3-δ(LSCrMC)掺杂30% CDC(CaO掺杂的CeO2)为阳极,La1-xSrxGa1-yMgyO3-δ(LSGM)为电解质,LSCF掺杂30%CDC为阴极的LSCrMC (CDC30%)| LSGM| LSCF (CDC30%)单电池开路电压为0.93V；LSCrMC (LSGM40%)| LSGM| LSCaFC (LSGM40%)单电池的开路电压随温度升高降低,最大功率密度随温度升高而增加,电池在850℃的开路电压为0.914V,最大功率密度为76mW/cm2。可以发现电池的开路电压较高,而功率密度较小。电池的制备工艺和电池材料的选择同等重要,电池的制备工艺有待优化。更多还原

【Abstract】 In the development of solid oxide fuel cell (SOFC) technology, one of the key problems is to improving the performance of electrodes at intermediate temperature (500℃-850℃). In this thesis, perovskite type oxides La1-xAxM1-yNyO3-δ(A=Sr, Ca; M and N=Fe, Mn, Co, Cu) were prepared and characterized to develop superior cathode materials for intermediate temperature solid oxide fuel cell (ITSOFC). The optimum conditions of preparation, the relation between structure and performance of the materials were investigated.Two methods were employed in material synthesis:EDTA complexing sol-gel method and glycine nitrite process. The materials including La1-xSrxCo1-yFeyO3-δ(LSCF), La0.8Sr0.2Co0.085CuxFe0.915-xO3-δ(LSCCuF), La0.8Sr0.2Co0.055FexMn0.95-xO3-δ(LSCFM) and La0.8Sr0.04Ca0.16Fe1-zCozO3-δ(LSCaCF) were studied.These materials were characterized by thermo gravimetric analysis (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microcopy (SEM), energy dispersive spectroscopy (EDS), temperature-programmed desorption of O2 (O2-TPD), X-ray photoelectron spectroscopy (XPS), characterization on the diameters of particles, the specific surface area mensuration, iodometric titration, electrochemical impedance spectra and direct current four-electrode techniques and so on.The optimum conditions of EDTA complexing sol-gel method are summarized as follow:the pH value of the solution should be adjusted to≥7; the mol ratio of metal ion to EDTA should be 1:1.1 to 1:1.2; the mol ratio of glycol to EDTA is 3:1; the concentration temperature should be 60℃-70℃; calcination temperature should be 700℃-800℃.All the powder samples prepared by EDTA complexing sol-gel method are perovskite-type compounds and no simple metal oxides or any other secondary phase exits in the structure. With the increase of Sr content, the main diffraction peaks of XRD move to large angles, which represent a distortion to small size of the cell. The powders are spherical shape and the powder can be identified to porous structure, with specific surface areas of about 11.6m2/g, total pore volume of 0.034cc/g and average pore diameter of 11.9nm. The particle is uniform with an average size of about 0.18μm by laser granularity analysis. Oxygen desorption from LSFC below 850℃was examined by O2-TPD and the result shows that there are three types of oxygen in the structure:adsorbed oxygen on surface, adsorbed oxygen in oxygen vacancy, lattice oxygen. The content of adsorbed oxygen on surface increase when Sr doped in A site and it seems that elements in B site have little influence to oxygen species. The La3d5/2 and O1s binding energy of the materials doped in both A and B site are lower than that only doped in A or B site, which indicate superior conductivity of double doped material.LSCF materials have good chemical compatibility with La1-xSrxGa1-yMgyO3-δ(LSGM) electrolyte.Pure perovskites are synthesized by both the two methods but morphology of powders have marked differences by comparison of EDTA complexing sol-gel method and glycine nitrite process. By EDTA complexing sol-gel method, the powders have small and uniform grain size. By glycine nitrite process, the powders have good porosity and large specific surface but more aggregate than by EDTA complexing sol-gel method. The remarkable dominance of GNP is the greatly shortened process.The La0.8Sr0.2Co0.085CuxFe0.915-xO3-δand La0.8Sr0.2Co0.05FexMn0.95-xO3-δpowders were prepared by the Glycine-Nitrate Process (GNP) method. The LSCCF-0.3 exhibits pure perovskite phase.The electrical conductivities of the La0.8Sr0.2Co0.085CuxFe0.915-xO3-δwere measured by a four point DC method. As the substitution amount of Cu increase, the electrical conductivity increases first and decreases later. The electrical conductivity of LSCCF-0.3 increases first and decreases later with the temperature increasing, and reach the maximum of 1809.47S/cm at 600℃. The electrical conductivity of LSCCF-0.3 in air is higher than in argon. There is no any second phase in the mixed powder of LSCCF-0.3 and 8YSZ after sintered at 800℃, but impurity phases form at 1000℃,1200℃. There is no any second phase in the mixed powder of LSCCF-0.3 and LSGM after sintering at 800℃, 1000℃and 1200℃initiate a small amount of La2SrFe2O7. By analysis, it illustrates that it is chemically compatible between the LSCCF-0.3 and LSGM.The La0.8Sr0.2Co0.05FexMn0.95-xO3-δpowders were measured by differential thermal analysis and thermogravimetry(TG-DTA) and the presintering temperature(1000℃, 2℃·min-1, 10h) was determined. The powder is pure perovskite phase by XRD analysis. It is found that the degree of oxygen non-stoichiometry (8) reduces with increasing x by the experiment of iodometric titration. The membranes have large density and no impurity-element is found through energy dispersion spectrometer (EDS). The conductivity measured by the four point DC method and the activation energy indicates that the conductive behavior of LSCFM agrees with the small-polaron hoping mechanism. The conductivity increases with the increasing temperature and reduces with increasing x, and besides, x=0 has the highest conductivity with 64.54S·cm-1 at 850℃.La1-x-ySrxCayFe1-zCozO3-δ(LSCaFC) fine powders have been synthesized by a glycine-nitrate process (GNP) method. The structure of La0.8Sr0.04Ca0.16CozFe1-zO3-δoxides were characterized to perovskite type oxides and the compositions are coincident with designed ratio. The oxygen non-stoichiometry values of La0.8Sr0.04Ca0.16CozFe1-zO3-δceramics increase with Co/Fe ration increase。The conductivity of LSCaFC materials increase with temperature increase and La0.8Sr0.04Ca0.16Co0.6Fe0.4O3-δmaterials have high conductivity of more than 100 S/cm from 550℃to 850℃. LSCaFC material have good chemical compatibility with LSGM electrolyte.The single cell with all perovskite materials was fabricated using LaCrO3-based, LaGaO3-based and LaFeO3-based materials as anode, electrolyte and cathode, respectively. The cathode films were prepared by two methodes:screen printing and co-sinter, spin coating and co-sinter. The maximum open circuit voltage of LSCrM | LSGM | LSCF (LSCrM50%) single cell is about 1.06V at 850℃using H2 and air as fuel and oxidant, respectively. The maximum open circuit voltage of LSCrMC (LSGM40%) | LSGM| LSCaFC (LSGM40%) and LSCrMC (CDC30%) | LSGM | LSCF(CDC30%) single cell is 0.914V and 0.93V respectively. The open circuit voltage value is similar to the theoretical electromotive force, shows the good cell sealing. But the maximum powder density is relatively small. The fabrication technique for single cell should be modified in the future.更多还原