中温固体氧化物燃料电池钴基钙钛矿阴极材料BaCaCoFeNbO的性能研究

发布时间：2018-03-04 04:00

  本文选题：中温固体氧化物燃料电池　切入点：B_(1-x)C_xCFN　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：能源是社会发展的基础,传统发电系统存在能源利用率低、高污染等诸多缺点,固体氧化物燃料电池(SOFC)具有转化效率高、污染低等诸多优点,是基于现有能源供应体系下可实现大规模高效发电的新能源技术。SOFC在发展之初存在操作温度(YSZ电解质操作温度为1000℃)过高的问题,因而引起材料易老化、成本过高及维护不便等一系列问题。SOFC实用化首先需要解决的问题就是其操作温度过高的问题,目前目标是把SOFC的操作温度降到中温(600-800℃)这一区间,但降低操作温度会增大电解质的欧姆损失以及阴极的极化损失。随着新型电解质材料的研发,欧姆损失得到降低,降低电解质材料的厚度也可以有效降低电解质的欧姆损失,近年来薄膜技术的发展对解决电解质欧姆损失的问题有较大贡献。因此,提高阴极材料在中温条件下的性能,即降低阴极材料在中温条件下的极化损失,提高在中温条件下的催化活性成为IT-SOFC发展的关键。本论文旨在通过改进现有阴极材料来提高IT-SOFC的性能。ABO_3型钴基钙钛矿氧化物的A位和B位阳离子可以被其他不同价态的的阳离子部分地取代,为保持整个体系的电中性而产生氧空位,使其在具有较高的电子导电性的同时具有良好的氧离子导电能力,是IT-SOFC其中一种非常重要的阴极材料。本文以Ba1-x Cax Co0.7Fe0.2Nb0.1O3-δ(BCCFN)阴极材料和BCCFN-SDC电解质复合阴极材料为研究对象,研究了阴极材料包括物相结构、微观形貌、热膨胀系数、半电池阻抗谱和单电池输出功率等各种特性。通过调控材料的成分组成,试图找出能降低阴极材料极化阻抗的配比,探讨其作为SOFC阴极材料的可行性,期望可以进一步提高IT-SOFC的性能。主要研究内容如下:1.钴基钙钛矿型氧化物Ba Co_(0.7)Fe_(0.2)Nb0.1O3-δ(BCFN)是一种电化学性能比较好的IT-SOFC阴极材料,其具有优秀的电子-离子混合导电能力。但其存在与电解质热匹配性较差的缺点,为了进一步提高此材料作为IT-SOFC阴极材料的性能,有必要降低其热膨胀系数,提高其与电解质材料的热匹配性,保证其在工作温度下的稳定性,降低其在中温(600-800 o C)下的极化阻抗,提升电极性能,从而提高单电池的最大功率密度。因此,我们选择在A位掺Ca~(2+)试图提高其作为IT-SOFC阴极材料的性能。采用固相法合成Ba1-xCax Co0.7Fe0.2Nb0.1O3-δ(B1-x Cx CFN,x=0.0,0.1,0.2,0.3,0.4)阴极材料,通过XRD衍射普分析发现,B1-xCx CFN阴极材料在1000 oC烧结10 h后,形成了单相的立方钙钛矿结构。通过分析电镜图片,B0.9C0.1CFN形成了疏松多孔的微观结构,并且与SDC电解质结合良好,没有出现剥落迹象。A位掺杂Ca~(2+)后,降低了阴极材料的热膨胀系数。半电池阻抗分析发现BCFN材料A位掺杂Ca~(2+)降低了阴极材料的极化电阻(RP),当A位掺Ca~(2+)的掺杂量为x=0.1时,RP值最小,在800 o C时,B0.9C0.1CFN半电池的极化电阻值为0.4458Ωcm2。Ca~(2+)的适当掺杂使B位离子从+3价升到+4价,使B3+-O-B4+小极化子的浓度提高,降低了材料的极化阻抗,电化学性能得到提高,当进一步提高Ca~(2+)的掺杂量时,B位离子从+3价升到+4价的离子数过多,+3价离子数减少,使材料的极化阻抗增加。单电池功率密度测试发现结构为B1-xCx CFN/SDC/Ni0.9Cu0.1-SDC的单电池随着阴极A位Ca~(2+)的掺入,功率密度变大,当Ca~(2+)的含量x为0.1时,以B0.9C0.1CFN为阴极材料的单电池具有最好的输出功率密度曲线,在800o C的最大功率密度达到338m Wcm-2,当进一步提高A为Ca~(2+)的掺杂量时,单电池的功率密度开始下降,B0.9C0.1CFN阴极表现出最好的电化学性能。2.B_(0.9)C_(0.1)CFN阴极材料表现出了优秀的综合性能,成为一种有希望的IT-SOFC阴极材料。为了进一步增强材料的电化学性能以及与SDC电解质的匹配性,提高氧的还原反应速率,我们对B0.9C0.1CFN材料进行了改进研究,将B0.9C0.1CFN(BCCFN)与SDC电解质材料复合制成复合阴极材料,可望进一步降低其热膨胀系数,改善阴极材料的氧还原反应过程,提高其性能。研究结果表明,1000 o C烧结10h后,BCCFN与SDC间保持各自的相结构,化学相容性良好。电镜图片显示BCCFN-30SDC表现了更低的空隙率及更小的颗粒尺寸,这有利于形成连续的SDC离子扩散通道和连续的BCCFN电子导电通道。复合SDC是一种可以有效降低阴极材料的热膨胀系数的方法,使其热膨胀系数更接近于SDC电解质,提高了阴极材料与电解质材料的热匹配性。BCCFN阴极材料复合SDC可以提高阴极材料的电化学性能,BCCFN-x SDC(x=0,20,30,40)复合阴极材料半电池阻抗测试表明,随SDC电解质的复合量的增加,阴极极化电阻(Rp)随之而减小,当复合含量x=30wt%时,极化电阻达到最小值,在800o C时Rp值达到0.2984Ωcm2,当SDC含量进一步增多时,BCCFN相连续性下降,影响了阴极氧的还原反应,使极化电阻反而增大。以BCCFN-x SDC为阴极的电解质支撑的结构为BCCFN-x SDC|SDC|Ni0.9Cu0.1-SDC的单电池的测试结果表明,复合SDC的含量为30wt%时,单电池表现出更优的功率密度曲线,800 o C时以BCCFN-30SDC为阴极的单电池最大功率密度达到351 m Wcm-2,这表明BCCFN-30SDC是一种发展前景良好的IT-SOFC阴极材料。
[Abstract]:Energy is the foundation of social development, has low energy utilization of traditional power system, high pollution and many other shortcomings of solid oxide fuel cell (SOFC) has the advantages of high conversion efficiency, low pollution, high efficiency of power generation is to achieve large-scale new energy technology.SOFC operating temperature at the beginning of the development of existing energy supply system based on the (the operation of YSZ electrolyte temperature of 1000 DEG C) high, and easy material aging, high cost and inconvenient maintenance of a series of practical problems in.SOFC to solve the first problem is that the operating temperature is too high, the current goal is to SOFC operating temperature to drop in temperature (600-800 DEG C) this interval. But the lower operating temperature will increase the electrolyte ohmic losses and cathode polarization loss. With the development of new electrolyte materials, ohmic loss can be reduced, the reduction of electrolyte material thickness It can effectively reduce the ohmic loss of electrolyte, in recent years the development of thin film technology to solve the problem of electrolyte ohmic losses have a greater contribution. Therefore, to improve the performance of cathode materials in temperature, which reduce the polarization loss of cathode material in the temperature, in high temperature catalytic activity become the key to the development of IT-SOFC. The purpose of this paper is to improve the existing cathode materials to improve the performance of.ABO_3 type cobalt oxides IT-SOFC A and B can be replaced by other cations of different valence cations in part, to keep the whole system of electrically neutral and oxygen vacancies, which has good conductivity of oxygen ion the higher electronic conductivity at the same time, IT-SOFC is one kind of cathode material is very important. This paper takes Ba1-x Cax Co0.7Fe0.2Nb0.1O3- 8 (BCCFN) and BCCFN-S cathode materials DC electrolyte composite cathode material as the research object, research on the cathode materials including phase structure, microstructure, thermal expansion coefficient, various characteristics of half cell impedance spectroscopy and single cell output power. By adjusting the material composition, trying to find out the material can reduce the cathodic polarization impedance ratio, to explore its feasibility as SOFC cathode material and look forward to further improve the performance of IT-SOFC. The main contents are as follows: 1. cobalt based perovskite type oxide Ba Co_ (0.7) Fe_ (0.2) Nb0.1O3- 8 (BCFN) is a kind of electrochemical performance of IT-SOFC cathode material is better, it has excellent electron ion conductivity. But the existence of mixed electrolyte matching and heat of the poor, in order to further improve the material properties of IT-SOFC as cathode material, it is necessary to reduce the thermal expansion coefficient, increase the heat and electrolyte materials matching, ensure the Stability at the working temperature, reduce the temperature in the (600-800 o C) polarization impedance of the electrode to enhance performance, thereby increasing the maximum power density of the single cell. Therefore, we chose A doped Ca~ (2+) to improve the performance of IT-SOFC as cathode material synthesized by solid phase method. Ba1-xCax Co0.7Fe0.2Nb0.1O3- Delta (B1-x Cx CFN, x=0.0,0.1,0.2,0.3,0.4) cathode materials by XRD diffraction analysis showed that the general B1-xCx, CFN cathode materials sintered at 1000 oC after 10 h, the formation of single phase cubic perovskite structure. Through the analysis of electron microscope images, B0.9C0.1CFN formed a micro porous structure, and SDC electrolyte with good, no peeling off signs of.A doped with Ca~ (2+), cathode material coefficient of thermal expansion is reduced by half. The cell impedance analysis showed that the BCFN material A doped with Ca~ (2+) to reduce the polarization resistance of the cathode material (RP), when the A doped Ca~ (2+) The doping amount is x=0.1, the minimum RP value at 800 o, C, B0.9C0.1CFN half cell polarization resistance value of 0.4458 ohm cm2.Ca~ (2+) the appropriate doped B ions from the +3 price rose to +4 price, the concentration of B3+-O-B4+ small polaron increase, reduce the polarization resistance of materials, electrochemical performance when improved, further improve the Ca~ (2+) doping, B ions from the +3 ion +4 price price to rise to excessive number of +3 ions decreased, the polarization resistance of materials increased. Single cell power density test showed that the structure is a single cell B1-xCx CFN/SDC/Ni0.9Cu0.1-SDC with A Ca~ (2+) cathode the incorporation of power density change, when Ca~ (2+) the content of X is 0.1, the single battery cathode material with B0.9C0.1CFN as the output power density curve with the best, the maximum power density in 800o C to 338m Wcm-2, when Ca~ further improve A (2+) doping amount, single cell the The power density began to decline, B0.9C0.1CFN cathode showed best electrochemical performance of.2.B_ (0.9) C_ (0.1) CFN cathode material shows excellent performance, has become a promising cathode materials for IT-SOFC. In order to further enhance the electrochemical performance of the material and the compatibility with the SDC electrolyte, improve the oxygen reduction reaction rate. We improved the study of B0.9C0.1CFN materials, B0.9C0.1CFN (BCCFN) and SDC electrolyte material made of composite cathode materials, is expected to further reduce the coefficient of thermal expansion, improve the cathode oxygen reduction reaction process, improve its performance. The results show that the 1000 o C 10h BCCFN after sintering, and SDC phase structure the chemical compatibility is good. Electron microscopy images showed that BCCFN-30SDC showed the particle size and smaller porosity lower, which is conducive to the formation of SDC ion channel and continuous diffusion 杩炵画鐨凚CCFN鐢靛瓙瀵肩數閫氶亾.澶嶅悎SDC鏄�涓�绉嶅彲浠ユ湁鏁堥檷浣庨槾鏋佹潗鏂欑殑鐑�鑶ㄨ儯�

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