【作者】 孔馨；

【导师】 丁锡锋；

【作者基本信息】 南京理工大学 ， 材料工程， 2012， 硕士

【摘要】 固体氧化物燃料电池(SOFC)作为一种高效、环保的绿色新能源受到全球广泛关注。当前研究的热点是降低固体氧化物的工作温度,开发中温固体氧化物燃料电池。中温(500℃-800℃)能避免固体氧化物燃料电池在高温环境下工作时会发生各界面的反应、电极热膨胀系数与电解质热膨胀系数不匹配造成的电池劈裂等问题,也能扩宽电极材料的选择范围,避免使用贵金属,降低电池成本,加快其商业化运用。然而随着工作温度的降低,电极的电化学性能会急剧降低。因此开发高催化活性的新型中温固体氧化物阴极材料具有重要意义。AA’B2O5+δ层状钙钛矿是一类混合离子电子导体(MIEC)。层状结构为氧离子提供了有序的扩散通道,其表面扩散系数和表面交换系数都高于传统的ABO3立方钙钛矿,这种结构特点使得AA’B2O5+δ层状钙钛矿氧化物成为一种潜在的中温固体氧化物阴极材料。本论文采用溶胶凝胶法合成了新型铜基层状钙钛矿氧化物LnBaCu2O5 (Ln= La、Nd、Sm)、LnBa0.5Sr0.5Cu2O5(Ln=Nd、Sm、Gd)、SmBaCuMO5+δ(M=Fe、Ni、Zn),研究探讨了A、B位掺杂对其性能的影响。并采用离子浸渍法制备复合阴极SBCO-SDC,优化了微观结构。论文首先研究了LnBaCu2O5 (Ln= La、Nd、Sm)氧化物。物相分析显示在1000℃烧结制备的LnBaCu2O5 (Ln= La、Nd、Sm)均为纯相。LnBaCu2O5 (Ln= La、Nd、Sm)在50-800℃的平均热膨胀系数为13～14.6×10-6/℃,比传统的Co基层状钙钛矿氧化物(17～21×10-6/℃)热膨胀系数小,更接近中温电解质热膨胀系数。随稀土离子半径的降低,LnBaCu2O5 (Ln= La、Nd、Sm)电化学性能提高。在700℃时,SmBaCu2O5+δ的极化电阻仅为0.48Ωcm2。其次研究了Sr掺杂对LnBaCu2O5结构和性能的影响。在LnBaCu2O5(Ln=Nd、Sm、Gd)的A’位掺杂Sr不会改变其晶体结构,Sr掺杂可以明显提高新型层状钙钛矿型阴极材料LnBaCu2O5电导率,降低其极化电阻。SmBa0.5Sr0.5Cu2O5的电导率在485℃时达到了277.7 S·cm-1。LnBa0.5Sr0.5Cu2O5阴极极化电阻较低,SmBa0.5Sr0.5Cu2O5的极化电阻降低了约50%。在550℃极化电阻仅为0.19Ωcm2,Sr掺杂主要改善了氧离子的扩散能力。然后探究了B位掺杂过渡金属元素对Cu基层状钙钛矿性能的影响。SmBaCuFeO5+δ和SmBaCuNiO5+δ为纯相,但SmBaCuZnO5+δ含有第二相CuO。SmBaCuMO5+δ(M=Fe、Ni、Zn)热膨胀系数在14～16×10-6/℃之间。交流阻抗分析SmBaCuFeO5+δ电化学性能最优,750℃时,SmBaCuFeO5+δ极化电阻最小,为0.54Ωcm2,但是其电导率较小。通过Sr掺杂,提高了SmBaCuFeO5+δ的电导率和电化学性能,SmBa0.5Sr0.5CuFeO5+δ极化电阻Rp在650℃为1.05Ωcm2,比SmBaCuFeO5-δ(650℃为2.75Ωcm2)降低了2.5倍。最后采用离子浸渍法制备复合阴极材料SBCO-SDC,优化了微观结构。通过SEM观察到在SBCO阴极骨架上生成了纳米级的SDC颗粒,扩大了三相反应界面区。复合阴极SBCO-SDC存在一个最佳浸渍范围,浸渍量为3.83%的SBCO-SDC在600℃时的极化电阻仅为0.63Ωcm2,而同等条件下,未浸渍的SBCO极化电阻为1.19Ωcm2。浸渍片最佳烧结温度为900℃。更多还原

【Abstract】 Solid oxide fuel cells (SOFC) have been received increasing attention recently because of its clean energy conversion and high energy efficiency. The high operating temperature (1000℃) leads to some problems, such as the serious interface reaction, possible crack formation due to the mismatch of thermal expansion coefficient(TEC) of the cell component and so on. Reducing the operating temperature to intermediate temperature (500℃-800℃) would have several advantages, such as wider use of low-cost materials, reducing the solid-state reaction between the cell components. However, the electrochemical activity of the cathode dramatically decreases with reducing temperature. Developing new mixed conductors, optimizing cathode microstructure between cathode and electrolyte interfaces are approaches of improving stable cathodes for IT-SOFC.AA’B2O5+δlayered perovskite oxides is a kind of mixed ionic and electronic conducting (MIEC) oxide. A-site is rare earth elements, A’-site is alkaline earth element and B-site is transition elements. Layered perovskite oxides consist of consecutive layer [BO2]-[AO]-[BO2]-[A’O] stackes along c-axis. Such layered structure reduces the oxygen bonding strength in [AO] layer, provides disorder-free channel for ion motion which enhance oxygen diffusivity.The chemical diffusion coefficient D and the surface exchange coefficient K in layered perovskite oxides were much higher than that of simple ABO3-type perovskite.The layered perovskite oxide powers LnBaCu2O5 (Ln=La,Nd,Sm), LnBa0.5Sr0.5Cu205(Ln=Nd,Sm,Gd),SmBaCuMO5+δ(M=Fe,Ni,Zn) were synthesized by a combined citrate and EDTA complexion method. The effects of performance by A-site and B-site doping were systematically investigated. Composite cathodes SBCO-SDC were prepared by impregnation method.The XRD results of LnBaCu2O5 (Ln= La,Nd,Sm) showed that all the powers which sintered at 1000℃obtained as a single structural phase. The thermal expansion coefficients (TEC) of LnBaCu2O5 (Ln= La、Nd、Sm) were 13-14.6×10-6/℃in 50℃-800℃, which were more compatible with electrolyte than cobalt-based cathodes. The LnBaCu2O5 (Ln= La、Nd、Sm) oxides show a increase in cathode performance with decreasing size of Ln3+ ions. Polarization resistance of SBCO is 0.48 Qcm2 at 700℃.The conductivity of layered perovskite LnBaCu2O5 was significantly improved by Sr doping. And the polarization resistance was reduced as well. The maximum electrical conductivity of SmBa0.5Sr0.5Cu2O5 was 277.7 Scm-1, about one order of magnitude higher than that of SmBaCu2O5+δ. Polarization resistance (0.19Ωcm2) of SBSCO at 550℃is twice lower than that of SmBaCu2O5+δ(SBCO). Sr doping improved the oxygen ion diffusion during oxygen reduction reaction (ORR).The effect of B-site transition matal elements on layered perovskite performance was investigated. It was obtained that SmBaCuFeO5+δand SmBaCuNiO5+δas single structural phase while SmBaCuZnO5+δhad the CuO phase. The TEC of SmBaCuMO5+δ(M=Fe、Ni、Zn) were about 14～16×10-6/℃in 50℃-800℃. The electrochemical performance of SmBaCuFeO5+δwas best by AC impedence analysis. Polarization resistance of SmBaCuFeO5+δis 0.54 Qcm2 at 750℃. The conductivity and electrochemical performance had been improved by Sr doping for SmBa0.5Sr0.5CuFeO5+δ. Polarization resistance of SmBa0.5Sr0.5CuFeO5+δis 1.05 Qcm2 at 650℃, which is much smaller than that of SmBaCu2O5+δ(2.75Ωcm2 at 650℃).Composite cathodes SBCO-SDC were synthesized by impregnation method and its microstructure is optimized. It was observed by SEM that nano SDC particles were generated on the skeleton of SBCO, which expanded the three-phase boundary (TPB) for ORR. There is an optimum range of impregnation for composite cathodes SBCO-SDC. The polarization resistance of SBCO-SDC with 3.83wt% SDC was 0.63Ωcm2 at 600℃,while polarization resistance of SBCO without impergiatation was 1.19Ωcm2 at the same temperature. And the optimum sintering temperature for impregnated film was 900℃.更多还原