氧化物对LSCF阴极氧还原速率影响的研究

发布时间：2018-03-06 02:23

本文选题：固体氧化物燃料电池　切入点：阴极　出处：《中国科学技术大学》2015年博士论文　论文类型：学位论文

【摘要】：固体氧化物燃料电池(SOFC)是清洁高效的能源利用装置。它的效率主要制约于阴极的氧还原反应。本文以典型的阴极催化剂La1-xSrxCo1-yFeyO3-δ(LSCF)为对象,研究氧化物对其催化性能即阴极氧还原速率的影响规律,包括掺杂氧化铈、碱土元素的氧化物和过渡元素氧化物等,以增强氧还原动力学,提高中温SOFC的输出性能。第一章阐述了SOFC电解质,阳极,阴极等关键材料的种类和性质。重点介绍阴极材料及结构,特别是用浸渍法制备的含纳米粒子的阴极。介绍了纳米结构阴极的长期稳定性,分析了纳米结构阴极的制备过程和纳米颗粒生长的理论模型,同时针对不同种类的阴极材料,分析了其纳米结构的电化学性能和稳定性。第二章发现,掺杂氧化铈(SDC, SmxCe1-xO2-δ)能够明显增强LSCF上的氧还原动力学,SDC粒子可将LSCF的表面交换系数Kchem提高5倍。K-chem随着SDC粒子的负载量增加到最大值后降低,表明SDC的增强效应与SDC, LSCF和气相的三相线相关。K-chem与SDC的组成相关,在同样的负载量下,K-chem随着x先增加后降低,当x=0.2时达到最大值；进一步分析发现,Kchem与SDC的离子电导率6线性相关,即随着6的增加而增加。结果表明,SDC的自由氧空位促进了氧在LSCF表面的还原反应动力学。此外,氧还原反应的活化能基本不变,表明SDC没有改变LSCF表面的氧还原机理。第三章发现碱土金属化合物的氧还原反应的增强作用。首先,BaCO3纳米颗粒显著地提高了LSCF、LSF (La0.8Sr0.2FeO3-δ)和LSM (La0.8Sr0.2MnO3-δ)等阴极催化剂的表面氧还原反应速率。在BaCO3粒子的作用下,LSF和LSCF的Kchem都有一个数量级的增大。进一步分析发现,LSF电极的低频阻抗减小约数量级,例如,700℃时从2.54Ωcm2减小到0.26Ωcm2。Kchem的增大与低频阻抗的减少,说明BaCO3主要是提高了氧的吸附解离等表面过程。以LSF阴极,YSZ(Y0.15Zr0.85O2-δ)电解质,Ni-YSZ阳极构成的单电池,阴极浸渍BaCO3纳米颗粒后,800℃下的峰值功率输出从0.3Wcm-2增大到0.53Wcm-2。此外,BaCO3纳米颗粒提高了电极的稳定性,在7000C下、380h的测试过程中,纯LSF电极的极化阻抗增长约90%,即从2.96Qcm2增大到5.48Ωcm2,而在LSF电极中浸渍了BaCO3纳米颗粒后,界面极化阻抗基本维持在0.84Ωcm2。同时,微结构分析表明,在热处理过程中,BaCO3纳米颗粒的形貌未发生任何变化。其次,作为LSF的协同催化剂,CaO粒子展现出了特殊的性质。表面浸渍CaO粒子后,LSF的Kchem增大约10倍,但是,其界面极化阻抗没有减少,反而增大。进一步分析发现,代表氧离子传输的高频阻抗明显增大,而与表面过程相关的低频阻抗减小。如果LSF电极中的氧离子传输分为体相和表面路径,而CaO粒子阻碍了02-的表面传输。使用离子导体SDC与LSF混合,形成LSF-SDC复合阴极,解决了氧离子传输问题。750℃C下,以YSZ为电解质,浸渍3.01wt%CaO后,LSF-SDC复合电极的极化阻抗从0.83Ωcm2减小到0.42Ωcm2。浸渍CaO粒子后,单电池的输出功率密度也增加,800℃C从0.45Wcm-2增大到0.58Wcm-2。最后,SrO的作用与BaCO3、CaO均不相同,在La0.8Sr0.2FeO3-δ(LSF113)催化剂表面浸渍SrO,会形成La0.8Sr1.2FeO4-δ(LSF214), LSF214是一种An+1Bn03n+1结构的Rullesden-Popper(RP)相,由于其独特的钙钛矿层和盐岩层排布,具有较高浓度的氧空位和电化学催化活性。因此,浸渍后构成具有核壳结构的催化剂(LSF214壳-LSF113核)。与纯相LSF113相比较,这种核壳结构的Kchem提高接近15倍,并进一步降低界面极化电阻。XPS分析表明,LSF214颗粒只形成在LSF113颗粒的外表面。通过浸渍-反应途径,形成LSF214-LSF113核壳结构,是构建异质结构电极的可能方法。第四章初步研究了过渡金属元素(Cr、Mn、Fe、Ni、Zn、Co、Cu等)氧化物对LSCF的催化的影响。电导弛豫结果表明,Cr的氧化物降低了LSCF表面的氧还原反应速率,造成阴极中毒。其余氧化物均提高了反应速率,其中Cu的增强效应最大,Kchem提高约20倍。利用真空蒸镀技术,在LSCF表面蒸镀不同含量的CuO,同时利用SEM确定CuO的表面覆盖率θCuO以及单位LSCF面积上的三相线长度LTPB,研究Kchem与CuO蒸镀量和微结构的关系。CuO增强的表面交换系数KCuO与θCuO和LTPB均不成严格的线性关系,说明CuO增强作用可能同时发生在CuO的表面和CuO-LSCF-气相的三相线上。在测试温度范围内,CuO对整个氧还原反应的贡献率λCuO,随着温度的升高而增大。800℃C下,LTPB为1.14cm-1时,λCuO为30%,而当LTPB为增大到14.7cm-1时,CuO的贡献率接近80%。在CuO浸渍的LSCF电极中,其极化阻抗明显降低,650℃C下浸渍8.5wt%CuO后,极化阻抗从0.76Ωcm2减小到0.51Ωcm2。阻抗谱分析表明,低频阻抗明显减少。在以SDC为电解质的单电池中,使用CuO浸渍的LSCF阴极,650℃C输出功率密度从0.55Wcm-2增大到0.75Wcm-2。
[Abstract]:Solid oxide fuel cell (SOFC) is a clean and efficient energy utilization device. Its efficiency is mainly restricted to the cathodic oxygen reduction reaction. The cathode catalyst La1-xSrxCo1-yFeyO3- 8 typical (LSCF) as the research object, the oxide on the catalytic performance of the cathodic oxygen reduction effect of rate, including doped cerium oxide, alkaline earth elements oxides and transition element oxides, in order to enhance the kinetics of oxygen reduction, improve the output performance of temperature in SOFC.
The first chapter of the SOFC electrolyte, anode, cathode, kinds and properties of key materials. Focusing on cathode materials and structure, especially prepared by impregnation with nanoparticles. The long-term stability of nano cathode cathode structure, analysis of the preparation of nano structure of cathode process and the theoretical model of nanoparticle growth, at the same time according to the different kinds of cathode materials, electrochemical properties and stability of the nano structure is analyzed.
The second chapter found that doped ceria (SDC, SmxCe1-xO2- 8) significantly enhanced the LSCF on the kinetics of oxygen reduction, SDC particles can be LSCF surface exchange coefficient Kchem increased 5 times with.K-chem loading of SDC particles increases to a maximum and then decreased, and SDC showed that the enhancement effect of SDC,.K-chem and three phase composition SDC LSCF and the correlation of the load in the same way, with the K-chem x first increased and then decreased, when x=0.2 reaches the maximum value; further analysis showed that the ionic conductivity of Kchem and SDC 6 linear correlation with 6 increases with the increase of free oxygen vacancies. The results showed that SDC promoted the oxygen the kinetics of the reduction of the LSCF surface. In addition, the oxygen reduction reaction activation energy is basically unchanged, suggesting that SDC did not change the LSCF surface mechanism of oxygen reduction.
The third chapter found that alkaline earth metal compounds enhanced oxygen reduction reactions. Firstly, BaCO3 nanoparticles significantly increased LSCF, LSF (La0.8Sr0.2FeO3- 8) and LSM (La0.8Sr0.2MnO3- 8) surface oxygen cathode catalyst. In the reaction rate of BaCO3 particles under the action of LSF and LSCF Kchem are an order of magnitude the increase. Further analysis shows that the low frequency impedance of LSF electrode decreases about magnitude, for example, 700 degrees from 2.54 ohm cm2 reduced to 0.26 ohm cm2.Kchem decreased with the increase of low frequency impedance, indicating that BaCO3 is mainly improved oxygen adsorption solution from the surface to the cathode process. LSF, YSZ (Y0.15Zr0.85O2- 8) electrolyte Ni-YSZ, single cell anode composition, cathode impregnated with BaCO3 nanoparticles, the peak power output at 800 DEG C increased from 0.3Wcm-2 to 0.53Wcm-2. in addition, BaCO3 nanoparticles improves the stability of the electrode, in 7000C, 380h test During the test, the polarization resistance of LSF electrode increased by about 90%, which increased from 2.96Qcm2 to 5.48 cm2, while in LSF electrode impregnated with BaCO3 nanoparticles, the interfacial polarization impedance maintained simultaneously in 0.84 ohm cm2., the microstructure analysis shows that in the process of heat treatment, the morphology of BaCO3 nanoparticles did not occur any change.
Secondly, as a co catalyst LSF, CaO particles exhibit special properties. The surface impregnation of CaO particles, LSF Kchem increased by about 10 times, but the interface polarization impedance is not reduced, but increased. Further analysis showed that the high frequency impedance representing oxygen ion transport increases significantly, while the low frequency impedance associated with the surface process decreased. If oxygen ion transport in LSF electrode into the bulk phase and surface path, while the CaO particles hinder the surface transfer 02-. Using SDC and LSF mixed ion conductor, the formation of LSF-SDC composite cathode, solve the transmission problem of oxygen ion.750 C C, with YSZ as the electrolyte, after 3.01wt%CaO impregnation, the polarization resistance of LSF-SDC the composite electrode decreases from 0.83 cm2 to 0.42 Omega Omega cm2. impregnated CaO particles, the output power density of single cell increased, C 800 degrees increased from 0.45Wcm-2 to 0.58Wcm-2.
Finally, effect of BaCO3 and SrO, CaO are not the same, in the La0.8Sr0.2FeO3- Delta (LSF113) surface impregnation catalyst SrO, will form La0.8Sr1.2FeO4- 8 (LSF214), LSF214 is a An+1Bn03n+1 structure of the Rullesden-Popper (RP), because of its unique calcium titanium ore layer and rock salt layer distribution, oxygen vacancy and electrochemical catalytic activity with a higher concentration. Therefore, after impregnation catalyst with core-shell structure (LSF214 shell -LSF113 core). Compared with pure LSF113, the core-shell structure of Kchem increased nearly 15 times, and further reduce the interfacial polarization resistance.XPS analysis showed that LSF214 particles formed in the outer surface of LSF113 particles through. The impregnation reaction path, the formation of LSF214-LSF113 core-shell structure, is a possible method to construct heterojunction electrode.
The fourth chapter studied the transition metal elements (Cr, Mn, Fe, Ni, Zn, Co, Cu etc.) the influence of catalytic oxide on LSCF. The results show that the conductivity relaxation, Cr oxide reduced LSCF surface oxygen reduction reaction rate caused by poisoning of cathode. The rest of the oxides increased the reaction rate. The enhancement effect of Cu, Kchem increased by about 20 times. Using vacuum evaporation technique, on the surface of LSCF coating with different content of CuO, while using SEM to determine the CuO surface coverage of three line length LTPB and theta CuO unit LSCF area, a strict linear relationship between the surface of Kchem and.CuO enhanced relations CuO evaporation amount and the micro structure of the exchange coefficient KCuO and 9 CuO and LTPB are not, CuO enhancement may also occur on the surface of CuO and CuO-LSCF- gas phase in the test line. The temperature range of CuO for the oxygen reduction reaction of the contribution rate of lambda CuO, with temperature The increase of.800 C C, LTPB 1.14cm-1, a CuO of 30%, while the LTPB was increased to 14.7cm-1, the contribution rate of CuO is close to 80%. in LSCF CuO impregnated electrode, the polarization resistance decreased obviously under 650 DEG C after 8.5wt%CuO impregnation, the polarization resistance of cm2 decreases from 0.76. 0.51 ohm cm2. impedance analysis results show that the low-frequency impedance decreased. In SDC single cell as the electrolyte in the cathode of LSCF using CuO impregnation, 650 DEG C output power density increased from 0.55Wcm-2 to 0.75Wcm-2.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：O643.36;TM911.4

【共引文献】