中温固体氧化物燃料电池钴基钙钛矿阴极材料BaCoFeNbO的性能与反应过程研究

发布时间：2018-04-22 02:18

  本文选题：固体氧化物燃料电池 + 氧的还原反应　； 参考：《吉林大学》2016年博士论文

【摘要】：固体氧化物燃料电池(SOFC)由于其清洁、高效的特点已经受到世界越来越广泛的关注,成为了未来能源系统中不可或缺的电源装置。传统的SOFC由于操作温度过高(1000 oC),容易引起材料老化、材料间界面反应及高的成本投入等问题。有效的解决这些问题的途径是降低SOFC的操作温度(600-800 oC)。但电解质的欧姆损失,特别是阴极的极化损失也随着操作温度的降低显著增大。随着电解质新型材料和薄膜技术的研发,已基本解决了电解质的欧姆损失问题。因此,提高阴极的催化活性,降低阴极的极化损失成为了降低电池操作温度的关键,是中温固体氧化物燃料电池(IT-SOFC)发展的重要方向。分析阴极反应机制,优化阴极反应步骤,进而提高阴极反应速率是提高催化活性的重要途径。通过发展新型电极材料提高电化学反应速率是当今IT-SOFC研究的主线之一。ABO3型钴基钙钛矿氧化物具有较高的电子-离子混合导电能力与氧催化还原能力,成为了IT-SOFC的主要阴极材料。本文以钴基混合导电阴极材料和电解质复合阴极材料为主要研究对象,研究了材料的化学组成、微观结构、反应机制等因素对阴极性能产生的影响。通过调控材料的组成与结构,对材料性能优化的可行途径进行探索,并探讨了影响材料电化学性能的规律与物理、化学本质,旨在分析出阴极的氧的还原反应步骤,找到降低阴极极化损失,提高阴极催化活性的关键,并为促进IT-SOFC的发展提供一定的材料与技术储备。主要研究内容如下:1.钙钛矿型氧化物Ba Co0.7Fe0.2Nb0.1O3-δ(BCFN)具备很好的电子-离子混合导电能力,作为IT-SOFC阴极材料表现出了较好的电化学性能。但是,影响此材料性能的主要因素,氧的还原反应的主要步骤,以及控制反应速率的主要过程仍没有系统的研究。因而,为了进一步探索BCFN材料的整体反应过程,提高氧的还原反应速率,提升阴极性能,我们选择在A位掺Sr来分析其性能优化的可行性和根本原因。采用固相法合成Ba1-x Srx Co0.7Fe0.2Nb0.1O3-δ(B1-x Sx CFN,x=0.0,0.1,0.2,0.3,0.4)阴极材料,研究发现,B1-x Sx CFN材料在1000 oC烧结10 h后,形成了单相的立方钙钛矿结构。掺杂之后,材料的热膨胀系数降低。阴极的极化电阻(RP)随着Sr的掺杂量先减小后增大,当Sr的掺杂量为x=0.2时,RP值最小。Sr的适当掺杂提高了小极化子的浓度,使小极化子和氧空位达到了最佳浓度比,材料的导电能力增强,电化学性能提高。电化学反应机制研究表明,阴极上的反应包括氧的解离吸附和扩散过程;氧原子得电子生成氧离子过程;氧离子在三相界面处和氧空位结合生成晶格氧过程。对没掺Sr的BCFN样品,在氧分压1 atm-0.01 atm变化范围内,限速步骤为氧原子得电子生成氧离子过程;而对于Sr的掺杂量为0.2的B0.8S0.2CFN样品,在氧分压大于0.1 atm时,氧原子得电子生成氧离子过程为限速步骤,当氧分压小于0.1 atm时,限速步骤为氧的解离吸附和扩散过程。电解质支撑的单电池B1-xSx CFN/SDC/Ni0.9Cu0.1-SDC的功率密度随着Sr含量的增多,先增大后减小,当Sr的含量x为0.2时,表现出最好的电化学性能。2.B0.8S0.2CFN作为IT-SOFC阴极材料表现出了优异的性能。为了增强材料的离子导电性,提高氧的还原反应速率,我们对B0.8S0.2CFN材料进行了相应的改性研究,将电解质材料SDC与B0.8S0.2CFN(BSCFN)混合制成复合阴极材料,目的是改善氧的还原反应过程,提高阴极性能。研究结果表明,BSCFN与SDC间没有相反应,化学相容性良好。复合后热膨胀系数降低,与电解质SDC的热膨胀系数更加接近,提高了阴极与电解质的热匹配性。SDC的加入改善了材料的微观结构,拓展了三相界面的长度,改善了材料的电化学性能,当复合30 wt.%SDC时阴极表现出最好的性能,在800 oC时其RP比纯BSCFN阴极的RP小很多。利用交流阻抗谱技术对比研究了BSCFN阴极和BSCFN-30SDC复合阴极在SDC电解质上的反应机制,研究结果表明:氧分压大于0.05 atm时氧离子和氧空位结合生成晶格氧过程为限速步骤,氧分压小于0.05 atm时氧的解离吸附和扩散过程为限速步骤。复合后阴极的电化学活性增强的主要原因为复合后反应速率的加快,SDC离子导电相的引入使得反应过程由三步缩短为两步,氧原子得电子后直接和氧空位结合生成晶格氧,大大提高了反应速率,阴极上的氧的还原反应活性增强。800 oC时,电解质支撑的单电池BSCFN-x SDC|SDC|Ni0.9Cu0.1-SDC的功率密度分别为620.37,656.79,717.56和663.00 m Wcm-2,这表明BSCFN-30SDC是很有前景的IT-SOFC阴极材料。3.在BCFN这类电子-离子混合导电材料中,电子电导往往比离子电导高几个数量级,因而进一步提高阴极性能的一种有效途径就是提高离子电导率。引入A位离子缺陷对钙钛矿型阴极材料的晶体结构、氧空位浓度和热膨胀系数都可能产生影响,进而改变阴极的反应过程。因而,我们采用固相法制备了Ba1-xCo0.7Fe0.2Nb0.1O3-δ(B1-xCFN,x=0,0.05,0.10,0.15)系列阴极材料,通过XRD、SEM、交流阻抗谱以及单电池的测试,研究其A位缺位对晶体结构、热膨胀以及电化学反应的影响。研究发现,B1-xCFN经过1000oC烧结10个小时后,完全形成立方钙钛矿结构,晶胞体积随着A位缺位量的增加并不呈线性变化关系,B0.9CFN的晶胞体积最大,说明A位离子的缺陷更多的是产生氧空位,而不是使B位金属离子升价。随着缺位量的增加,孔隙率下降,B0.9CFN阴极的孔隙率最小。当缺位量增加为0.15时(即B0.85CFN),由于颗粒团聚使得孔隙率增加。随着A位Ba含量的减少,界面极化电阻减小,当x=0.10时,即B0.90CFN在800oC时,界面极化电阻下降约66.2%。在氧分压大于0.01 atm时,氧离子和氧空位结合生成晶格氧过程为限速步骤,当氧分压为0.01 atm时,氧的解离吸附和扩散过程为限速步骤。Ba缺陷引起的氧空位的增多,使得氧原子得电子后直接和氧空位结合生成晶格氧,反应速率提升,阴极的氧的还原反应活性增强。半电池的阻抗谱和单电池性能结果显示,在800 oC时B0.90CFN表现出良好的阴极催化活性。4.为了继续提升材料中的离子电导率,我们采用在材料中复合离子导电的电解质的方法。研究结果表明,经1000 oC烧结10个小时后,复合材料中的B0.9CFN和SDC仍保持各自相结构,没有杂相生成。电化学反应机制研究表明,氧分压大于0.05 atm时氧离子和氧空位结合生成晶格氧过程为限速步骤,氧分压小于0.05 atm时氧的解离吸附和扩散过程为限速步骤。其电化学性能提高的原因为:离子导电相SDC的加入影响了氧原子得电子后和氧空位生成晶格氧的电荷转移过程和氧的解离吸附和扩散过程,加快了这两个过程的反应速度。当SDC的含量达到30 wt.%时,复合阴极具有最小的RP。复合后阴极材料的孔隙率增加,B0.9CFN-30SDC具有足够的孔隙率和合适的颗粒尺寸。阴极内部形成连续的B0.9CFN导电相的同时也形成了连续的SDC离子扩散通道。
[Abstract]:Solid oxide fuel cell (SOFC) has been paid more and more attention in the world because of its clean and efficient characteristics. It has become an indispensable power device in the future energy system. Traditional SOFC is easy to cause material aging, intermaterial interface reaction and high cost input due to the high operating temperature (1000 oC). The way to solve these problems is to reduce the operating temperature of SOFC (600-800 oC). However, the ohm loss of the electrolyte, especially the polarization loss of the cathode, is also significantly increased with the decrease of operating temperature. With the development of new electrolyte materials and film technology, the problem of Ohm loss in electrolytes has been solved basically. Therefore, the catalysis of the cathode is improved. The key of reducing the operating temperature of the battery is the activity of reducing the polarization loss of the cathode. It is an important direction for the development of the medium temperature solid oxide fuel cell (IT-SOFC). The analysis of the mechanism of the cathode reaction, the optimization of the cathodic reaction step, and the improvement of the reaction rate of the cathode are an important way to improve the catalytic activity. The improvement of the new electrode material is improved. The electrochemical reaction rate is one of the main lines of current IT-SOFC research..ABO3 Co based perovskite oxide has high electronic and ion mixed conductivity and oxygen catalytic reduction ability. It has become the main cathode material of IT-SOFC. This paper studied the Co based mixed cathode materials and electrolyte complex cathode materials as the main research object. The effects of the chemical composition, microstructure and reaction mechanism of the material on the performance of the cathode were investigated. The feasible way to optimize the properties of the materials was explored by regulating the composition and structure of the materials, and the laws and the physical and chemical nature of the electrochemical properties of the materials were discussed, in order to find out the steps of the reduction reaction of the oxygen in the cathode. The key to reduce the cathodic polarization loss and improve the catalytic activity of the cathode is to provide a certain material and technical reserve for the development of IT-SOFC. The main contents are as follows: 1. the perovskite type oxide Ba Co0.7Fe0.2Nb0.1O3- Delta (BCFN) has good electrical and ionic mixed electrical conductivity, which shows good electricity as a IT-SOFC cathode material. However, the main factors affecting the properties of the material, the main steps of the oxygen reduction reaction and the main process of controlling the reaction rate are still not systematically studied. Therefore, in order to further explore the overall reaction process of the BCFN material, improve the rate of oxygen reduction reaction and improve the performance of the cathode, we choose to analyze the A bit with Sr. The feasibility and fundamental reason for its performance optimization. Ba1-x Srx Co0.7Fe0.2Nb0.1O3- Delta (B1-x Sx CFN, x=0.0,0.1,0.2,0.3,0.4) cathode material was synthesized by solid phase method. It was found that B1-x Sx CFN material formed a single-phase cubic perovskite structure after 1000 oC sintering of 10 h. After doping, the thermal expansion coefficient of the material was reduced. The polarization of the cathode was polarized. When the doping amount of Sr is reduced first and then increased, when the doping amount of Sr is x=0.2, the proper doping of RP value.Sr increases the concentration of the small polaron, which makes the small polaron and the oxygen vacancy reach the optimum concentration ratio, the electrical conductivity of the material is enhanced and the electrochemical performance is improved. The electrochemistry reaction mechanism study shows that the reaction on the cathode includes oxygen. The process of dissociation adsorption and diffusion; oxygen atoms generate oxygen ions by electrons; oxygen ions combine with oxygen vacancies to produce lattice oxygen processes at the three-phase interface and oxygen vacancies. In the range of oxygen partial pressure of 1 atm-0.01 ATM, the speed limiting step for oxygen atoms to generate oxygen ions by oxygen atoms, while the doping amount of Sr is 0.2 B0.8S0.. 2CFN sample, when oxygen partial pressure is greater than 0.1 ATM, oxygen atom generates oxygen ion process as a speed limiting step. When oxygen partial pressure is less than 0.1 ATM, the speed limit step is oxygen dissociation adsorption and diffusion process. The power density of the electrolyte supported single cell B1-xSx CFN/SDC/Ni0.9Cu0.1-SDC increases with the increase of Sr content, and then decreases, when the Sr content is contained. When the amount of X is 0.2, the best electrochemical performance.2.B0.8S0.2CFN shows excellent performance as a IT-SOFC cathode material. In order to enhance the ionic conductivity of the material and increase the rate of the oxygen reduction reaction, we have made a corresponding modification to the B0.8S0.2CFN material, and mixed the electrosolution material SDC and B0.8S0.2CFN (BSCFN) into the composite. The purpose of the cathode material is to improve the reduction process of oxygen and improve the performance of the cathode. The results show that there is no reaction between BSCFN and SDC, and the chemical compatibility is good. The thermal expansion coefficient of the composite decreases and the thermal expansion coefficient of the electrolyte SDC is closer, and the thermal matching of the cathode and the electrosolution is improved by the addition of.SDC. The structure expands the length of the three-phase interface and improves the electrochemical performance of the material. When the composite is 30 wt.%SDC, the cathode shows the best performance. At 800 oC, the RP is much smaller than the RP of the pure BSCFN cathode. The reaction mechanism of the BSCFN cathode and the BSCFN-30SDC composite cathode on the SDC electrolyte is compared by the AC impedance spectroscopy, and the results of the study are studied. It is shown that the process of oxygen ion and oxygen vacancy combined to produce lattice oxygen is a speed limiting step when oxygen partial pressure is greater than 0.05 ATM, and oxygen partial pressure is less than 0.05 ATM, the dissociation adsorption and diffusion process of oxygen is the speed limiting step. The main reason for the electrochemical activity enhancement of the composite cathode is the acceleration of the recombination reaction rate and the introduction of the SDC ion conductive phase. The process is shortened from three steps to two steps, and the oxygen atom is directly combined with the oxygen vacancy to generate lattice oxygen, which greatly improves the reaction rate. When the oxygen reduction reaction on the cathode increases.800 oC, the power density of the electrolyte supported single cell BSCFN-x SDC|SDC|Ni0.9Cu0.1-SDC is 620.37656.79717.56 and 663 m Wcm-2, respectively. The bright BSCFN-30SDC is a promising cathode material for the IT-SOFC cathode material.3. in the BCFN type electron ion mixed conductive material, the electronic conductance is often several orders of magnitude higher than the ionic conductance. Therefore, an effective way to further improve the performance of the cathode is to improve the ionic conductivity. The crystal junction of the Perovskite Cathode material is introduced by the introduction of the A ionization defect. The oxygen vacancy concentration and thermal expansion coefficient may affect the reaction process of the cathode. Therefore, we have prepared the Ba1-xCo0.7Fe0.2Nb0.1O3- Delta (B1-xCFN, x=0,0.05,0.10,0.15) series cathode materials by solid phase method. Through the XRD, SEM, AC impedance spectroscopy and single battery test, the crystal structure and thermal expansion of the A bit vacancy on the crystal structure were studied. The effect of expansion and electrochemical reaction was found. It was found that the cubic perovskite structure was completely formed after B1-xCFN 1000oC sintering for 10 hours. The cell volume was not linearly dependent on the increase of the A bit vacancy, and the largest cell volume of B0.9CFN showed that the defects of A bit ions were more than the B bit metal ions. With the increase of the vacancy, the porosity decreases and the porosity of the B0.9CFN cathode is the smallest. When the vacancy increase is 0.15 (B0.85CFN), the porosity increases because of the particle agglomeration. With the decrease of A Ba content, the polarization resistance of the interface decreases. When x=0.10, B0.90CFN at 800oC, the interfacial polarization resistance decreases about 66.2%. at oxygen partial pressure. At 0.01 ATM, the formation of lattice oxygen by oxygen ions and oxygen vacancies is a speed limiting step. When the oxygen partial pressure is 0.01 ATM, oxygen dissociation adsorption and diffusion process is the increase of oxygen vacancy caused by the speed limiting step.Ba defect. The oxygen atom is formed into lattice oxygen directly and oxygen vacancy, and the reaction rate increases and the oxygen reduction of the cathode is reduced. The reaction activity was enhanced. The impedance spectrum of the semi battery and the performance of the single cell showed that at 800 oC B0.90CFN showed a good cathodic catalytic activity.4. in order to continue to improve the ionic conductivity in the material. We adopted a method of conducting a composite ion conductive electrolyte in the material. The results showed that the composite material was prepared after 1000 oC sintering for 10 hours. The B0.9CFN and SDC still maintain their respective phase structure and have no phase formation. The electrochemical reaction mechanism studies show that oxygen ion and oxygen vacancies combine to produce lattice oxygen process when oxygen partial pressure is greater than 0.05 ATM is a speed limiting step, and oxygen partial pressure is less than 0.05 ATM, the dissociation adsorption and diffusion process of oxygen is a limiting step. The reason for the improvement of electrochemical performance is that the oxygen partial pressure is less than 0.05 ATM The addition of the ionic conductive phase SDC affects the process of charge transfer and the dissociation adsorption and diffusion process of oxygen atom after the electrons and oxygen vacancies produce the lattice oxygen. The reaction speed of the two processes is accelerated. When the content of SDC reaches 30 wt.%, the porosity of the cathode material with the minimum RP. composite is increased, B0.9CFN-30S DC has enough porosity and suitable particle size. A continuous B0.9CFN conductive phase is formed inside the cathode, and a continuous SDC ion diffusion channel is formed.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TM911.4
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本文编号：1785163