【作者】 王志成；

【导师】 翁文剑；

【作者基本信息】 浙江大学 ， 材料学， 2008， 博士

【摘要】 中低温固体氧化物燃料电池（Solid oxide fuel cell,SOFC）是当前能源领域研究的热点。本文针对电解质的薄膜化、阴极微观结构优化和抗积碳的阳极微观结构设计三个中低温SOFC面临的关键问题,选用Sm掺杂的CeO₂（SDC）作为电解质材料,采用阳极支撑的SOFC电池模式,引入纳米结构对电极微观结构进行改进和设计,并对电池电极的制备及性能展开了系统的研究。主要的研究内容如下:（1）为了降低电解质SDC陶瓷的烧结温度,文中分别选用了燃烧法和喷雾干燥热解法两种制备方法制备了纳米尺寸的SDC粉末。用硬脂酸燃烧法制得的SDC粉末,其晶粒尺寸和粒度分布明显受到硝酸根和硬脂酸的摩尔比（N/s）的影响。当N/s摩尔比为1:1.5时,制得的SDC粉末具有最小的晶粒尺寸（10～40 nm）和粒度分布。而且用硬脂酸制得的SDC前驱粉末是低结晶度的SDC粉末,比750℃热处理形成的SDC具有更小的粒度分布和更好的烧结性,在1200℃烧结温度下即可获得平均晶粒为0.85μm的致密SDC陶瓷。采用了（NH₄）₂CO₃（AC）和NH₄HCO₃（HC）沉淀剂制备了两种溶胶,用溶胶喷雾干燥热解法制备了SDC粉末。不同溶胶会对SDC粉末的粒径和形貌产生影响。用AC溶胶制得的SDC粉末具有较小的粒径和规则的球形形貌,从而可表现出良好的烧结特性,在1250℃温度下可烧结成相对密度达96%、晶粒尺寸为0.86μm的致密SDC陶瓷。（2）为了获得NiO和SDC两相分布均匀的纳米阳极材料,通过溶胶喷雾干燥热解法,采用了两种溶胶混合液来制备的NiO-SDC粉末,一种用Ni溶胶与Ce-Sm溶液混合,另一种用Ce-Sm溶胶与Ni溶液混合。结果表明:当用两种不同的溶胶混合液制备NiO-SDC粉末时,NiO-SDC阳极粉末的颗粒大小均随溶胶浓度的增加而增大。而且,用含Ni溶胶的混合液更易制得两相分布均匀,颗粒尺寸较小的NiO-SDC阳极粉末。一次颗粒尺寸为30 nm左右,团聚体的平均尺寸为250 nm。此外,还用氨基乙酸法制得了两相分布均匀的NiO-SDC粉末。其一次颗粒的平均粒径为20～40 nm,而且球磨后的粉末具有较窄的粒度分布,平均团聚尺寸为170 nm。（3）为了使阳极具有良好的多孔微观结构,在中低温下既具有良好的催化活性又可作为单电池的支撑体。本文采用聚苯乙烯微球作为造孔剂,利用造孔剂颗粒和纳米阳极材料颗粒在粒径上的较大差异,结合超声分散作用,使造孔剂颗粒和阳极材料均匀混合和合理分布,制备出可作为阳极支撑体的NiO-SDC多孔陶瓷。通过对多孔陶瓷的烧结温度、微观结构和力学性能之间关系的研究发现,1200℃烧结制得陶瓷的晶粒并没有明显长大并部分保持在纳米尺度范围内,使电极有相当长的三相反应界面长度,而且陶瓷的抗压强度达到了20.83 MPa。以此阳极为支撑的单电池在600℃时的最大输出功率密度高达333 mWcm^-2。高的电池功率密度说明该阳极微观结构可有效地提高其催化活性、降低其极化电阻,并抵消了因烧结温度较低而导致的电解质欧姆电阻升高所产生的负面影响。（4）采用纳米结构的阴极薄层的设计,解决中低温下电池阴极极化电阻迅速增大问题。选用具有较高离子电导和电子电导的SSC与SDC的纳米混合粉末作为阴极材料,采用悬浮液旋涂法制备了具有纳米结构的阴极薄层。实验结果表明:当烧结温度为950℃时,获得的阴极具有均匀连续的多孔结构,其孔隙率为31%,在阴极的骨架上大量的纳米晶粒,晶粒尺寸为50～100 nm,为气体的吸附和脱附提供较大的表面积;同时,阴极中均匀分布的SSC和SDC两相有利于提高阴极中的三相反应界面,增加反应活化点,有效地降低界面极化电阻,提高电池的功率输出。具有纳米多孔结构阴极薄膜的单电池在低温条件下表现出了良好的电性能。500℃时,单电池的整个界面电阻仅有0.79Ωcm²,最大输出功率密度高达212 mW cm^-2,450℃时则分别为2.81Ωcm²和114 mW cm^-2。（5）利用Cu单质具有抑制甲烷直接氧化产生碳沉积的能力,将少量纳米Cu颗粒均匀的分布到Ni/SDC陶瓷的骨架上,使铜的作用最大化,形成一种新的Cu/Ni/SDC阳极结构。本文采用浸渍法将Cu的纳米颗粒注入,使其紧密地粘附在多孔Ni/SDC陶瓷的骨架上。纳米Cu的注入提高了阳极的电导率,为更多的电子能够从电化学反应点的导出提供了有效的通道,从而了增加单电池的功率输出。当以甲烷气体为燃料时,Cu/Ni/SDC阳极支撑的单电池在600℃时的功率输出高达317 mW cm^-2。当单电池运行12h后,其最大输出功率密度只损失了2%。Cu/Ni/SDC阳极能够通过降低阳极中Ni的表面积和CO的不均匀分解来抑制碳沉积,使单电池输出功率具有长期稳定性。通过研究Cu对碳氢气体催化机理的研究发现,阳极中的铜参与了燃料的电化学反应,对燃料的氧化起到了催化作用。其催化作用主要通过在金属Cu与SDC的界面处的Cu₂O实现的。更多还原

【Abstract】 Nowadays,intermediate/low temperature solid oxide fuel cells（SOFCs）have attracted many attentions in the resaerch of power sources area.Main research works concentrate on the following areas,such as preparing thin electrolyte membranes on the electrodes,optimizing the electrode microstructure and developing new anode materials and new structures for hydrocarbon with high electrochemical catalytic activity at low temperature and strong ability to suppress carbon deposition.This thesis focuses on the above mentioned issues to carry out studies on the anode-supported SOFC with Sm doped CeO₂ as electrolyte through designing and preparing nanostructured electrodes.These researches are summarized as:（1）In order to reduce the sintering temperature of Ce_0.8Sm_0.2O_1.9（SDC）ceramic, nanocrystalline SDC powders were prepared by both a combustion process and a colloidal seed-assisted spray drying and pyrolysis method.SDC powders were prepared by a novel solution combustion process using molten stearic acid as dispersive medium and reducing agent.The particle size and distribution of SDC powders were influenced by the molar ratio of NO₃^- to stearic acid（N/s）.The powders prepared with the molar ratio of N/s at 1:1.5 exhibited a narrower distribution in size and the average agglomerate size was about 157 nm.The primary particle size was in the range 10～40 nm.The as-combusted powders showed a low crystallinity and exhibited an excellent sintering performance,easily achieving high dense SDC ceramics with lager grains（0.85μm）.The nanocrystalline SDC electrolyte powders were prepared by colloidal seed-assisted spray drying and pyrolysis.（NH₄）₂CO₃（AC）and NH₄HCO₃（AHC）were used as precipitation reagents to prepare colloidal solutions,and SDC powders with different particle size and morphology were obtained.The SDC powders prepared with AC colloidal solution showed spherical in morphology and smaller particle size, which showed excellent sintering behavior and could be sintered up to 96%of the theoretical at a lower sintering temperature of 1250℃,and the average grain size of ceramics was 0.86μm.（2）In order to obtain nanosized anode materials with uniform distribution of NiO and SDC,nanocrystalline NiO-SDC composite powders were prepared by the colloidal spray drying and pyrolysis method.Two series of mixed colloidal solutions were prepared.One contained Ni sols and Ce-Sm solution;the other contained Ce-Sm sols and Ni solution.The results showed that the primary particle size of the NiO-SDC composite powders slightly increased with the concentration of spray mixed colloidal solutions.Furthermore,the composite powders from mixed colloidal solutions with Ni sols showed more uniform distribution of two phases and smaller particle size than those from mixed colloidal solutions with Ce-Sm sols.The primary particle size was about 30 nm amd the powders had a very narrow particle size distribution centered at 250 nm.In addition,The NiO-SDC powders were also synthesized by a glycine-nitrate method.The ball-milled powders became fine particles with 20-40 nm for primary particle size,and 170 nm for average agglomerated particle size and a narrower distribution in sizes.（3）In order to obtain the anode with high catalytic activity at intermediate/low temperature,the porous NiO-SDC ceramics were prepared with monodispersed polystyrene（PS）spheres as the pore template,which was used as the anode in the anode-supported SOFCs.Considering the difference in the particle size between PS spheres and NiO-SDC powders,the powders and PS spheres were mixed under ultrasonic in ethanol to make them mixed and distributed uniformly.The relations among sintering temperature,microstructure and mechanical strength of the ceramics were studied.The results indicated that the NiO-SDC ceramic sintered at 1200℃showed to have an interconnected pore structure,about 150 nm grains in the pore walls,and the compression strength with 20.83 MPa.The maximum power density as high as 333 mWcm^-2was obtained operated at 600℃.The high power output showed that such an anode could provide high surface areas and more catalytically active sites and counteract the negative influence of the increasing ohmic resistance in electrolyte.（4）To reduce the cathode-electrolyte interfacial polarization resistance of low temperature SOFCs,a nanostructured porous thin cathode consisting of Sm_0.5Sr_0.5CoO₃（SSC）and SDC was fabricated on an anode-supported electrolyte sheet（membrane）using spin-coating technique.A suspension with nanosized cathode powders,volatilizable solvents and a soluble pore former was prepared.In the cathode, the SDC grains distributed uniformly on and cross the SSC matrix.The cathode had a good interconnecting porous structure with the porosity about 31%and there were many 50～100 nm grains on the frameworks.The results indicated that the cell with the nanostructured porous thin cathode sintered at 950℃showed relatively high maximum power density of 212 mW cm^-2at 500℃and 114 mW cm^-2at 450℃,and low interfacial polarization resistance of 0.79Ωcm² at 500℃and 2.81Ωcm² at 450℃.The good performance is attributed to that the nanostructured porous thin cathode can provide high surface area for gas adsorption/desorption and has high triple-phase boundaries（TPBs）length,which increases the electrochemical reactions sites and decreases the interfacial polarization resistance effectively.（5）Considing the strong ability of Cu to suppress the carbon deposition when dry methane is directly oxidized in anode,a Cu/Ni/SDC anode was designed.The anode was prepared by the impregnation method,whereby a small amount of Cu was incorporated into the previously formed Ni/SDC porous matrix.Cu nanoparticles adhered to and were uniformly distributed on the pore surface of the Ni/SDC prous matrix,and maximized the role of Cu in suppressing carbon deposition.The higher electronic conductivity of Cu/Ni/SDC anode was obtained,which provided the effective passage for more electrons to be transported from the electrochemical reaction sites so that the power output of the cell can be enhanced.For the resulting Cu/Ni/SDC anode-supported cell,maximum power density of 317 mW cm^-2was achieved at 600℃.The power density showed only～2%loss after 12-h operation. The results demonstrate that the Cu/Ni/SDC anode effectively suppresses carbon deposition by decreasing the Ni surface area available and the level of carbon monoxide disproportionation.This combination of effects results in very low power density loss over the operating time.According to the catalytic mechanism of Cu to the hydrocarbon,it was found that Cu participates in the electrochemical reaction of the fuel and the catalysis of Cu was carried out through Cu₂O at the interface between Cu and SDC.更多还原