摘要
固体氧化物燃料电池(SOFC)是一种高效环保的电化学能源转换器件。中温化是目前国际SOFC领域的研究热点及发展趋势。然而，工作温度的降低会导致阴极材料催化活性的大幅度下降，成为制约中温SOFC发展的关键瓶颈之一。钴基钙钛矿材料具有良好的中温催化活性，但其与电解质的热、化学匹配性较差。本论文旨在提高阴极的中温反应活性，发展了一种新型、高性能电催化活性的SOFC阴极材料——尖晶石CuCo2O4，并对其物理化学性质、与电解质的相容性、电催化活性等进行了全面的表征。实验中进一步通过与高氧离子传导电解质复合构建了多种微结构的复合电极，深入研究探索了其反应机制、微结构与电化学性能之间的构效关系。
通过溶胶凝胶法制备CuCo2O4纳米粉体。研究结果表明，当柠檬酸(CA)与乙二胺四乙酸(EDTA)的摩尔比增加至1:1.5时，可得到单相的立方晶相尖晶石CuCo2O4材料，材料晶粒尺寸小，约为70-200 nm，颗粒大小均匀。该材料与SSZ电解质具有较好的化学相容性，在50-900 ˚C范围内的平均热膨胀系数11.76×10-6 K-1，与氧化钪稳定的氧化锆(SSZ)电解质热匹配性较好。在研究阴极烧结温度、造孔剂对CuCo2O4阴极微观形貌的影响规律基础上，得到最优的制备条件：阴极烧结温度为1000 ˚C，淀粉添加25 wt.%。在800 ˚C时，极化电阻为0.12 Ω·cm2，单电池的最大功率密度972 mW·cm-2。
为了提高CuCo2O4阴极的电催化反应活性，增加CuCo2O4阴极中的三相反应界面长度，研究中，在阴极
中引入10 mol% Sc2O3稳定的ZrO2 (SSZ) 和Ce0.9Gd0.1O1.95 (GDC) 氧离子传导材料。采用机械混合法制备复合阴极，CuCo2O4-SSZ复合阴极和CuCo2O4-GDC复合阴极的平均热膨胀系数分别为11.39-11.86×10−6 K−1和11.83-12.20×10−6 K−1，与SOFC组件中其他组件热匹配性较好。电化学测试结果表明，随着复合阴极中氧离子电解质含量的增加，可有效地增加阴极中的三相反应界面长度，复合阴极化电阻减少，但含量过多时，会导致扩散电阻增加，导致极化电阻反而增大。其中，GDC的复合量为60 wt.%时，复合阴极的性能最佳，在800 ˚C时，阴极的极化电阻为0.09 Ω·cm2，当电流密度为0.5 A·cm-1时，CuCo2O4-GDC60复合阴极的阴极过电位为74 mV。单电池最大输出功率提高到1074 mW·cm-2，展现出良好的稳定性。
为了改善CuCo2O4阴极的性能，采用离子浸渍法原位制备CuCo2O4/SSZ
纳米结构复合阴极。研究中考察了浸渍液的浓度、浸渍量及烧结温度对浸渍阴极微观结构的影响，得到浸渍液为0.025 mol/L时，浸渍CuCo2O4颗粒更均匀，浸渍4-5次，相对也较少。浸渍量为17.6 wt.%时，浸渍CuCo2O4效果较好。研究中发现烧结温度对浸渍CuCo2O4颗粒长大的影响不是很大，这可能是由于浸渍法制备材料过程中，热分解较低(360 ˚C)。同时，SSZ多孔骨架有效地抑制了CuCo2O4的长大过程，保证了CuCo2O4没有出现粗化等现象。最终得到的纳米复合阴极结构稳定，SSZ多孔骨架有效
地增加了三相反应界面区域和长度，提升CuCo2O4纳米阴极的氧化原催化活性，电化学性能得到明显提升，最佳浸渍量为17.6 wt.%的浸渍阴极具有最小的极化电阻，在800 ˚C为0.08 Ω·cm2，单电池最大输出功率为1136 mW·cm-2。同时，对浸渍CuCo2O4浸渍阴极的氧还原反应机制进行研究，得出氧离子在电极或从电极到电解质的三相反应界面的扩散过程是该电极反应的速率控制步骤。
关键词：固体氧化物燃料电池；阴极材料；CuCo2O4；复合阴极；纳米阴极
Abstract
Solid oxide fuel cell (SOFC) is    a kind of high efficiency and environmentally friendly electrochemical energy conversion device. Currently, intermediate-temperature solid oxide fuel cell (IT-SOFC) represents theresearch mainstream in international SOFC field. However, the lower temperature reduce catalytic activity of cathode materials, which the one of key bottlenecks confine the development of IT-SOFC. Although cobalt-based perovskite materials reveal good catalytic activity at intermediate-temperature, its thermal and chemical matching are poor with the electrolyte. To improve the performance of cathode, a new type of SOFC cathode was developed in this thesis, spinel CuCo2O4, which has a considerable electrocatalytic activity. The physical and chemical properties, the compatibility with the electrolyte, the electrocatalytic activity for oxygen reduction reaction (ORR) and t
he output performance of the battery were studied in detail. Furthermore, a variety of microstructural composite cathodes were constructed by introducing the high oxygen ion conducting electrolyte. Therefore, the relationship between reaction mechanism, microstructure and electrochemical properties were investigated.
Firstly, CuCo2O4 powders were prepared by sol-gel method. The results show that the pure cubic phase spinel CuCo2O4 is obtained when the molar ratio of CA to EDTA increases to 1:1.5. The grain size of the material is approximately 70-200 nm and the particle size is uniform. The CuCo2O4 material has good chemical compatibility with SSZ electrolyte. The thermal expansion coefficient of CuCo2O4is 11.76 ×10-6K-1in the range of 50-900 ˚C which matches with SSZ electrolyte. According to the influence of cathode sintering temperature and pore forming agent on CuCo2O4cathode, the optimum conditions were obtained as follows: the sintering temperature at 1000 ˚C and the starch content of 25%. The polarization resistance was 0.12 Ω·cm2 and the maximum power density of single cell was 972 mWcm-2 at 800 ˚C.
In order to further improve the electrocatalytic reactivity and increase the three-phase reaction interface length in CuCo2O4 cathode, 10 mol% Sc2O3 stabilized ZrO2(SSZ) and Ce0.9Gd0.1O1.95(GDC) oxygen ion conducting
materials were introduced into the cathode, and the composite cathodes were prepared by mechanical mixing method. The thermal expansion coefficient of CuCo2O4-SSZ and CuCo2O4-GDC composite cathodes were 11.39-11.86 * 10- 6 K-1and 11.83-12.20x 10-6K-1, respectively, which matching well with other SOFC components. The electrochemical test results show that the length of the three-phase reaction interface in the cathode can be effectively increased and the polarization resistance of the composite cathodes were decreased with the increasing oxygen ion electrolyte content in the composite cathode. However, when the content is too high, the diffusion resistance increased leading to polarization resistance increase. Among them, the composite cathode has the best performance when the composite content of GDC is 60 wt.%. At 800 ˚C, the polarization resistance is 0.09 Ω·cm2 and the cathode overpotential is 74 mV in current density0.5Acm-1of CuCo2O4-GDC60 composite cathode. The maximum output power of single cell is 1074 mWcm-2 with good stability.
To further improve the performance of CuCo2O4cathode, nanostructure CuCo2O4/SSZ composite cathode was prepared by in situ ion impregnation method. The effects of the concentration of impregnation solution, impregnation amount and sintering temperature on the morphology of the impregnated cathode were studied. The results show that the CuCo2O4particles were more uniform a
nd the impregnation times was relatively less (4~5) when the impregnation solution was 0.025 mol/L. The effect of impregnation CuCo2O4is better in the impregnation amount 17.6 wt.%. It is found that the influence of sintering temperature is not significant on the growth of CuCo2O4 particles because of the low thermal decomposition (360 ˚C) in the preparation of material by impregnation process. At the same time, SSZ porous skeleton effectively inhibited the growth process of CuCo2O4that ensure the CuCo2O4does not appear coarsening phenomenon and so on. Finally, the nano structure composite cathode is stable, and the SSZ porous framework effectively increased the interfacial area and length of the three-phase reaction, and enhances the catalytic activity of the nano CuCo2O4cathod. The electrochemical properties were improved significantly. The optimum immersion amount was 17.6 wt.%, which show the smallest polarization resistance at 800 ˚C for 0.08 Ω·cm2. The output power of single cell was 1136 mW cm-2. At the same time, the oxygen reduction
reaction mechanism of the CuCo2O4 impregnation impregnated was studied. It is illustrated that the oxygen ion in the electrode or from the electrode to the diffusion process of three phase reaction interface electrolyte is the rate controlling step of the cathode reaction.
reaction diffusionKeywords：Solid oxide fuel cell, Cathode material, CuCo2O4, Composite cathode, Nano cathode

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