B位离子掺杂钙钛矿型中温固体氧化物燃料电池阴极研究

发布时间：2018-04-27 16:56

本文选题：固体氧化物燃料电池 + 钙钛矿结构阴极材料　；参考：《大连理工大学》2015年博士论文

【摘要】：固体氧化物燃料电池(SOFC)是一种将化学能转变为电能的高效绿色能源技术,将SOFC工作温度由-1000℃高温降低至500℃-800℃中温范围,即研发中温SOFC,是目前该领域的重要发展方向。工作温度的降低有利于降低SOFC制备与运行成本、提高电池结构与性能稳定性进而延长使用寿命,但同时也带来阴极、电解质、阳极等组元材料的性能下降问题,特别是,由于阴极氧还原反应活化能较大,导致阴极极化阻抗随温度降低急剧增大,成为中温SOFC输出功率的主要限制因素。因此,研发综合性能优良的阴极材料对于促进SOFC中温化发展、应用具有重要意义。钻基钙钛矿结构氧化物是重要的中温SOFC阴极候选材料,具有高电子-离子混合电导率和高氧还原催化活性优势,但普遍具有过高的热膨胀系数(TEC),与常用电解质材料Gd0.1Ce0.9O1.95 (GDC). Sm0.1Ce0.9O1.95 (SDC)、La0.8Sr0.2Ga0.83Mg0.17O3-δ(LSGM)等存在TEC失配问题,将导致SOFC在高温烧结制备与长期运行过程中的结构开裂与性能恶化。因此,降低TEC值、提高与电解质材料的TEC匹配从而提高SOFC的结构与性能稳定性,是目前钴基钙钛矿阴极材料亟待解决的关键问题。钴基钙钛矿氧化物TEC高的本质原因来自于B位Con+(n=2、3、4)离子的还原变价以及电子自旋态的改变,以价态稳定的过渡金属离子部分取代Con+离子能够有效降低材料的TEC值；另外,在钴基钙钛矿氧化物中加入一定量TEC值小的其它组分构成复合阴极材料是降低TEC值的又一可行途径；并且,这两种TEC改性途径将同时伴随阴极电学与电化学性能的改变。本论文选择立方钙钛矿结构La0.5Ba0.5CoO3-δ与层状钙钛矿结构PrBaCo2O6-δ氧化物做为研究对象,通过进行B位离子掺杂与复合材料制备两种途径,进行该阴极材料性能优化研究。本论文的主要研究内容与实验结果如下：1、采用sol--l方法合成了B位Fen+(n=3、4)掺杂(LBCF-y,y=0.1-0.9)系列样品,并对LBCF-y的氧含量、化学缺陷、热膨胀行为、电学和电化学性能进行了研究分析。XRD结果表明：Fen+掺杂量y=0.1-0.7时,LBCF-y为立方钙钛矿结构纯相,y高于0.7则出现杂相,并且,随Fen+掺杂量增大,LBCF-y发生晶格膨胀；室温碘滴定测试结果表明：Fen+掺杂量越大,LBCF-y的氧含量与B位离子平均价态越高,当y=0.1-0.3时,晶格中B位离子主要以Fe4+、Co4+、Co3+形态存在,而对于y=0.5-0.7的样品,B位离子则主要以Fe4+、Fe3+、Co3+形态存在；在空气中20-1000-温度范围内测试了样品的热膨胀特性并计算了TEC值,随着Fen+掺杂量增大,LBCF-y的TEC值呈现先增大后减小趋势,在y=0.7时TEC最小；利用直流四电极方法测试了LBCF-y空气中100-850℃C温度范围内的电导率,发现电导率随温度的升高先增大后减小,而在相同温度下,随Fen+掺杂量增大,LBCF-y电导率逐渐降低,但所有样品电导率满足SOFC要求；LBCF-y TEC和电导率的变化规律与其化学缺陷随Fen+掺杂浓度的变化有关；测试了LBCF-y阴极在650-800℃C温度下与不同氧分压气氛中的交流阻抗谱特性,并探讨了电极反应机制,结果表明：随B位Fen+掺杂量增大,L BCF-y阴极极化阻抗有所增大,主要是由于Fen+掺杂降低了LBCF-y中的氧空位浓度,不利于LBCF-y阴极的高频氧离子体扩散；但是,所有LBCF-y (y=0.1-0.7)样品650℃下比表面极化阻抗(ASR)均小于01 Ω·cm2,具有高氧还原催化活性。2、采用sol-gel方法合成了B位Sc3+掺杂PrBaCo2-xScxO6-δ (PBCS-x, x=0.00-1.00)系列粉体,研究了Sc3+掺杂对样品的相结构、氧含量、化学缺陷、热学行为、热膨胀行为、电学及电化学性能等的影响。结果表明：随Sc3+掺杂量增大,样品发生相结构转变,低Sc3+掺杂量(x≤0.20)时,PBCS-x为四方相双层钙钛矿结构,SC3+掺杂量x=0.30-0.40时,为二元复合相,Sc3+掺杂量x=0.50-0.90时,为简单立方相钙钛矿结构,而Sc3+掺杂量过高(x=0.1)则出现少量杂相；碘滴定结果表明：随着Sc3+掺杂量增大,PBCS-x的氧含量减小,氧空位浓度增大,Co4+离子含量减小,该化学缺陷的变化是SC3+掺杂导致PBCS-x结构与性能变化的本质原因；随Sc3+掺杂量增大,PBCS-x TEC逐渐减小与电解质材料TEC匹配性提高,而电导率逐渐减小；PBCS-x/GDC/PBCS-x对称电池交流阻抗谱测试结果表明：Sc3+掺杂取代部分B位Co离子使PBCS-x阴极的电化学催化活性显著增强,阴极ASR随Sc3+掺杂量增大而减小,在所研究的PBCS-x系列样品中,Sc3一掺杂量x=0.5样品具有最好的电化学性能,600℃C时其ASR值仅为0.123 Ω·cm2,是一种具有应用前景的新型中温SOFC阴极材料。3、采用sol-gel方法制备了Pr0.83BaCo1.33Sc0.50δ-0.17PrCoO3(PBCS-0.17PCO)复合纳米粉体中温SOFC阴极材料,对其相结构、热膨胀系数、电学与电化学性能进行了研究,并与同成分单相阴极材料PrBaCo1.5Sco.506-δ进行了对比分析。XRD测试结果表明：该复合材料由两种立方相钙钛矿结构氧化物Pr0.83BaCo1.33Sco.5O6-δ与PrCoO3组成,其中PrCoO3含量为17 mo1%；微观形貌SEM图表明PBCS-0.17PCO复合样品具有颗粒尺寸小、粒度均匀、分散性好等的特点；TEC测试结果表明：与PrBaCo1.5Sco.5O6-δ单相阴极相比,PBCS-0.17PCO复合阴极TEC值减小,30-900℃C温度区间TEC值为18.4x10-6/℃,与电解质材料的TEC匹配性提高；利用直流四电极方法对样品在空气中50-850℃C温度下的电导率进行了测试,结果表明：PBCS-0.17PCO复合阴极电学行为与PrBaCO1.5Sc0.5O6-δ单相阴极不同,并且在整个测试温度区间内复合阴极的电导率相对较小；对称电池交流阻抗谱测试结果表明：PBCS-0.17PCO复合阴极具有良好的氧还原反应电化学催化性能,在600℃、650℃C、700℃、750℃下的ASR分别为0.127Ω·cm2、0.069Ω·cm2、0.039Ω·cm2、0.026Ω·cm2，且长时间工作性能稳定,是一种性能优良的新型中温SOFC复合阴极材料。
[Abstract]:Solid oxide fuel cell (SOFC) is a high efficient green energy technology that transforms chemical energy into electrical energy. It is an important direction in this field to reduce the working temperature of SOFC from -1000 C to 500 C and -800 C medium temperature range, which is an important direction of development in this field. The decrease of working temperature is beneficial to reduce the cost of SOFC preparation and operation and improve electricity. The stability of the pool structure and performance further prolongs the service life, but it also brings the performance decline of the cathode, electrolyte, anode and other component materials, especially, because the activation energy of the cathode oxygen reduction reaction is larger, the cathodic polarization impedance increases sharply with the temperature decrease, which is the main limiting factor of the output power of the medium temperature SOFC. The cathode materials with excellent comprehensive properties are of great significance for promoting the development of SOFC medium temperature. The drilling based perovskite structure oxide is an important medium temperature SOFC cathode candidate material, with high electron ion mixed conductivity and high oxygen reduction catalytic activity, but high thermal expansion coefficient (TEC) and common electrolyte materials are widely used. The Gd0.1Ce0.9O1.95 (GDC), Sm0.1Ce0.9O1.95 (SDC), La0.8Sr0.2Ga0.83Mg0.17O3- Delta (LSGM) and other TEC mismatches will lead to the structural cracking and performance deterioration of SOFC during the high temperature sintering and long-term operation. Therefore, the TEC value is reduced and the TEC matching with the electrolyte material is improved to improve the stability of the structure and performance of SOFC. At present, the key problem of cobalt based perovskite cathode material needs to be solved. The essence of cobalt based perovskite oxide TEC is due to the reduction price of B Con+ (n=2,3,4) ion and the change of electron spin state. The substitution of Con+ ions with the stable transition metal ions in the valence state can effectively reduce the TEC value of the material; in addition, in the cobalt base calcium carbonate, the cobalt base calcium oxide can be effectively reduced. It is another feasible way to reduce the TEC value by adding some other components with a certain amount of TEC value in the titanium oxide oxide. Moreover, the two TEC modification routes will be accompanied by the change of cathode and electrochemistry. This paper chooses the cubic perovskite structure La0.5Ba0.5CoO3- Delta and the PrBaCo2O6- delta oxygen of the layered perovskite structure. In this paper, the main research contents and experimental results are as follows: 1, the B bit Fen+ (n=3,4) doping (LBCF-y, y= 0.1-0.9) series samples were synthesized by sol--l method, and the oxygen content and chemical defects of LBCF-y were studied in this paper. The main contents and the experimental results of this paper were two ways. The thermal expansion behavior, electrical and electrochemical properties have been studied and analyzed by.XRD results. The results show that LBCF-y is a pure phase of cubic perovskite structure and Y is higher than 0.7 when the amount of Fen+ doping is y=0.1-0.7, and the lattice expansion of LBCF-y occurs with the increase of Fen+ doping amount. The test results at room temperature iodine drops show that the greater the doping amount of Fen+, the oxygen content of LBCF-y is found. The higher the average valence state of the B bit ion is, the B ions in the lattice are mainly in the form of Fe4+, Co4+, Co3+ when y=0.1-0.3, while for the samples of y=0.5-0.7, the B bit ions are mainly in Fe4+, Fe3+, Co3+ morphology, and the thermal expansion properties of the samples are measured in the range of 20-1000- temperature in the air and the values are calculated. The TEC value of BCF-y increases first and then decreases, and TEC is minimum at y=0.7. The conductivity of LBCF-y air in the temperature range of 100-850 C is measured by the method of DC four electrode. It is found that the conductivity increases first and then decreases with the increase of temperature, and the conductivity of LBCF-y decreases with the increase of Fen+ doping at the same temperature, but all samples are decreased. The electrical conductivity meets the requirements of SOFC; the variation of LBCF-y TEC and electrical conductivity is related to the change of the chemical defects with the Fen+ doping concentration; the impedance spectrum characteristics of the LBCF-y cathode at 650-800 C at C temperature and the different oxygen partial pressure atmosphere are tested and the electrode reaction mechanism is discussed. The results show that the L BCF-y negative is increased with the B bit Fen+ doping. The increase of polar polarization impedance is mainly due to the reduction of oxygen vacancy concentration in LBCF-y by Fen+ doping, which is not conducive to the diffusion of high frequency oxygen plasma of the LBCF-y cathode. However, all LBCF-y (y=0.1-0.7) samples are less than 01 Omega cm2 at 650 C, and have a high oxygen reduction catalytic activity.2, and B bit S is synthesized by the sol-gel method. C3+ doped PrBaCo2-xScxO6- Delta (PBCS-x, x=0.00-1.00) powders have been used to study the effects of Sc3+ doping on the phase structure, oxygen content, chemical defects, thermal behavior, thermal expansion behavior, electrical and electrochemical properties. The results show that the phase structure transformation of the sample increases with the increase of Sc3+ doping, and the PBCS-x is four when the low Sc3+ doping amount (x < 0.20) is low. In the double perovskite structure, when the SC3+ doping amount is x=0.30-0.40, it is two element composite phase, and when Sc3+ doping x=0.50-0.90, it is a simple cubic perovskite structure, while the Sc3+ doping amount is too high (x=0.1) appears a small amount of heterozygosity. The iodine titration results show that as Sc3+ doping increases, the oxygen content of PBCS-x decreases, the oxygen vacancy concentration increases, Co4+ ion concentration increases. The change in the chemical defect is the essential reason for the change of the structure and properties of PBCS-x with SC3+ doping. With the increase of the doping amount of Sc3+, the PBCS-x TEC decreases gradually with the electrolyte material TEC, and the conductivity gradually decreases, and the AC impedance spectroscopy test results of PBCS-x/GDC/PBCS-x symmetric batteries show that Sc3+ doping takes the place of partial B. The electrochemical catalytic activity of the PBCS-x cathode was significantly enhanced and the cathode ASR decreased with the increase of the doping amount of Sc3+. In the PBCS-x series of samples studied, the Sc3 doped x=0.5 samples had the best electrochemical performance. The ASR value was only 0.123 Omega cm2 at 600 C, and it was a new medium temperature SOFC cathode material.3, which was of the prospect of application. The medium temperature SOFC cathode material of Pr0.83BaCo1.33Sc0.50 Delta -0.17PrCoO3 (PBCS-0.17PCO) composite nano powder was prepared by sol-gel method. The phase structure, thermal expansion coefficient, electrical and electrochemical properties were studied. The comparison of the PrBaCo1.5Sco.506- delta with the single-phase cathode material of the same component was compared and analyzed by.XRD test results. The results showed that the composite material was the composite material. The material is composed of two kinds of cubic perovskite oxide Pr0.83BaCo1.33Sco.5O6- Delta and PrCoO3, of which the PrCoO3 content is 17 mo1%, and the micromorphology SEM diagram shows that the PBCS-0.17PCO composite samples have the characteristics of small particle size, uniform particle size and good dispersibility, and TEC test results show that, PBCS-0.1 compared with PrBaCo1.5Sco.5O6- delta single-phase cathode, PBCS-0.1 The TEC value of 7PCO composite cathode is reduced, the TEC value of C temperature range at 30-900 C is 18.4x10-6/ C, and the TEC matching of the electrolyte material is improved. The conductivity of the sample under the temperature of 50-850 C at 50-850 C in the air is tested by the direct current four electrode method. The results show that the PBCS-0.17PCO composite cathode electrical behavior is not with the PrBaCO1.5Sc0.5O6- delta single-phase cathode. The conductivity of the composite cathode is relatively small in the whole test temperature range, and the AC impedance spectroscopy test of the symmetrical battery shows that the PBCS-0.17PCO composite cathode has a good electrochemical catalytic performance in the oxygen reduction reaction, and the ASR at 650, 700, and 750 is 0.127 Omega. Cm2,0.039 Omega cm2,0.026 Omega at 650, 700 and 750. Cm2, which has long performance and stable performance, is a new type of medium temperature SOFC composite cathode material with excellent performance.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TM911.4

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