【作者】 范梁栋；

【导师】 王成扬； 朱斌；

【作者基本信息】 天津大学 ， 化学工艺， 2012， 博士

【摘要】 作为一种将化学能直接转化为电能的电化学装置，固体氧化物燃料电池（SOFC）或陶瓷燃料电池（CFC）因为有较高能源利用效率、低环境影响和燃料灵活等特点受到越来越多的关注。当前SOFC发展趋势是低温操作以降低系统的成本和提高其稳定性，从而与现有的能源转换方式相竞争。然而，低温操作需要高离子导电电解质和高催化活性电极，这已经成为发展低温SOFC的挑战课题,并极大限制了其商业化进程。掺杂氧化铈-碳酸盐复合材料的开发能有效地提高离子导电率和解决单相电解质材料一些缺陷，因此成为实现SOFC商业化的新途径。本论文从氧化铈-碳酸盐复合材料出发，研究了不同掺杂氧化铈前驱体对其电化学性能的影响；发展了Pr₂NiO₄-Ag和ZnO修饰的锂化氧化镍两种用于氧化铈-碳酸盐电解质基CFC的高效阴极材料；提出分析多离子导电体系离子导电研究普适方法-修饰的Wagner直流极化法。对氧化铈-碳酸盐复合物的离子导电率、混合离子导电行为和可能的离子导电机理以及基于复合电解质与不同电极材料的单电池的电化学性能进行了详细分析与研究，以达到对掺杂氧化铈-碳酸盐复合电解质材料的进一步理解和促进这类新型电解质材料的实际应用。主要研究结果如下：不同制备方法制备的钐掺杂氧化铈-（Li/Na）₂CO₃复合电解质材料因前驱体的不同在电化学性能有较大的差异。基于纳米复合方法制备的电解质拥有最小的颗粒尺寸和最均匀的物相分布，因此获得最高的离子导电性。以纳米复合方法获得的复合电解质基CFC在600℃给出了839mW·cm^-2的最大功率密度。采用柠檬酸燃烧法制备的次之，固相反应法最差，但是都远远高于SDC电解质基单电池的电化学性能。Pr₂NiO₄与复合电解质在650℃以下化学兼容良好。基于Pr₂NiO₄阴极的单电池在600℃具有652mW·cm^-2的最大功率密度，同其它钙钛矿阴极相比提高了很多，与经典锂化氧化镍阴极材料相当。添加10wt%活性Ag催化剂的Pr₂NiO₄-Ag复合材料降低Pr₂NiO₄电极的电荷转移和质量扩散阻抗，因此进一步提高了阴极的电催化活性。期望通过改善Ag浸渍工艺和组成获得更高的电化学性能。ZnO掺杂/复合后的锂化氧化镍颗粒变小、电导率降低，但其氧还原活性提高，阴极的电催化活性和单电池的功率密度输出也有一定程度的提高。600℃时获得了859mWcm-2的最大功率密度。使用修饰后电极的单电池在5h的恒外阻放电过程中保持稳定。氧化铈-碳酸盐中的本征O^2-和外源H⁺不同的离子传导特性导致不同的离子极化过程。采用交流阻抗谱在不同的气氛中的对欧姆阻抗的分析结果间接证实了混合的O^2-/H⁺导电性。提出的类似Wagner直流极化证实了O^2-和H⁺在复合电解质中的传导，该方法也可能成为研究复合材料体系中多离子导电行为的普适方法。直流极化测试结果证实复合电解质中O^2-电导率相对单相材料被提高了，而且H⁺电导率高于O^2-的电导率。因此氧化铈-碳酸盐复合电解质在燃料电池气氛下的高离子导电率是混合O^2-/H⁺导电的结果，也最终促成了低温下的高电化学性能。更多还原

【Abstract】 Solid oxide fuel cell （SOFC） or ceramic fuel cell （CFC）, an electrochemicaldevice that converts the chemical energy in fuels directly into electricity, has attractedgrowing attention because of its distinct advantages: high efficiency, lowenvironmental impact and fuel flexibility. The current SOFC research trend is todecrease the working temperature with the purpose of reducing the system costs andimproving the reliability. While the lowering operational temperature requires highionically conductive electrolyte and super-performance electrode materials, whichhave become barriers to significantly hinder the commercialization process of CFCs.The development of doped ceria oxide-carbonate composite electrolyte has effectivelyenhanced the ionic conductivity and solved some problems related with the single-phase electrolyte materials, which has demonstrated a new approach to realize thewide application of CFCs.In this dissertation, based on the ceria-（Li/Na）₂CO₃composite, we prepared andinvestigated the effects of the different SDC precursors on composites’ electricalproperties, developed and studied the performance of two kinds of novel electrodematerials-Pr₂NiO₄-Ag and lithiated transition metal oxides composites and applied amodified Wagner polarization method to study the complex multi-ionic conductiveproperties. The electrical properties, such as the ionic conductivity, mixed oxygenion/proton conduction behavior, the possible ionic conduction mechanism of SDC-carbonate composite and fuel cell performance for composite electrolyte CFCs withdifferent electrode materials are detailed analyzed. The main results are:The electrical properties of SDC-（Li/Na）₂CO₃composite electrolytes werehighly dependent on the SDC precursors which were prepared by nitrate-citriccombustion, solid-state reaction and modified nanocomposite （NANO） approaches,respectively. Among the composites, composite electrolyte by NANO approachexhibited the highest ionic conductivity and fuel cell performance. A maximum powerdensity of839mW·cm^-2was achieved at600℃under H₂/air atmosphere.The new developed Pr₂NiO₄（PNO） perovskite cathode catalyst showed a goodchemical compatibility with SDC-carbonate composite at and below650℃. Singlecell with PNO cathode delivered a peak power output of652mW·cm^-2at600℃withhydrogen as fuel and air as the oxidant, which was comparable with the common usedlithiated NiO cathode, while much higher in comparison with other perovskite oxides. The introduction of10wt%of Ag active catalyst into surface of PNO by infiltrationway not only improved the charge transfer rate but also raised the oxygen surfaceexchange kinetics, leading to a higher catalytic activity and subsequent an increasedelectrochemical performance. It is expected that the optimizations of the impregnationprocess and the electrode composition could further enhance the fuel cellperformance.The compositing or doping of ZnO reduced the particle size and the electricalconductivity while improved the oxygen reduction electro-catalytic activity oflithiated NiO. Peak power densities of600and859mW·cm^-2were achieved at500and600℃, respectively, in H₂/air condition. Moreover, single cell with modifiedcathode showed a stable performance during5h test under a constant externalresistance condition, indicating great promise for practical application.In SDC-carbonate composite, the ionic polarization process varied under oxygenand hydrogen atmospheres, which was attributed to the intrinsic and extrinsic ionicconducting properties, especially for oxygen ion and proton conduction. The ACimpedance spectroscopy measurements in different applied gas atmospheres offeredan indirect evidence for the mixed oxygen ion/proton conduction properties incomposite electrolyte, while the modified Wagner DC polarization approach clearlyshowed the oxygen ion and proton conduction in the SDC-carbonate composite. Themodified Wagner polarization method is also proposed as a universal approach tostudy the materials’ complex multi-ionic conduction properties. The results show thatthe proton conductivity in the SDC-carbonate composite is higher than oxygen ionicconductivity. Moreover, the oxygen ionic conductivity in composite electrolyte isenhanced compared with the single-phase electrolyte. The mixed oxygen ion andproton transports co-contribute the high ionic conductivity of the SDC-carbonatecomposite and subsequent high fuel cell electrochemical performance at the reducedtemperature.更多还原