【作者】 凌意瀚；

【导师】 陆亚林； 刘杏芹；

【作者基本信息】 中国科学技术大学 ， 材料学， 2013， 博士

【摘要】 能源与环境是当今人类社会可持续发展必须面对的两大难题。固体氧化物燃料电池(SOFC)是一种高效清洁的能量转换装置,在节能减排的能源市场大环境中具有广阔的发展潜力。为满足商业化对低成本和长寿命的要求,SOFC的操作温度必须由传统的高温(800-1000℃)向中低温范围(400-800℃)发展。但随着操作温度的降低,中低温SOFC的应用发展面临新的挑战,其中急需解决的重要问题包括：1)传统阴极材料在中低温条件下催化活性低,使电池输出功率较低；2)现有的中温电解质材料在操作条件下存在一定的电子导电现象,造成电池内短路,转换效率低；3)氢气燃料气储存运输困难,不适用作商业化燃料,而传统的阳极材料对碳氢燃料裂解具有高催化活性,易形成碳淀积,导致电池性能骤减。针对中低温SOFC的发展需求,本论文将(1)探讨阴极反应过程的关键影响因素,进而研发中低温下具有高催化活性的新型阴极材料；(2)探索发展低成本的电子阻隔层制备技术及发展具有高离子电导率和低电子电导率的新型电解质材料,以解决电池的内短路问题；(3)发展可直接用于碳氢化合物、煤基合成气、生物质气等燃料的新型阳极,降低SOFC的使用成本。本论文的主要内容和结果如下：第一章：简单介绍SOFC的研究背景、基本工作原理及国内外研究进展。从材料应用和发展的角度,着重阐述了SOFC实现中低温化发展所面临的重大挑战,并提出了本论文的研究目标及相关内容。第二章：针对中低温阴极材料电化学催化活性较低的现象,探索和发展了一系列中低温SOFC阴极材料,如LaBaCuCoO5+x(LBCC)、LaBaCuFeO5+x (LBCF)、 Sm0.5Sr0.5Fe0.8Cu0.2O3-δ(SSFCu)、SrFe0.9Sb0.iO3-δ(SFSb)和Ni0.7Co0.3O(NC3O)等。研究结果表明：1)Co基掺杂比铁基掺杂具有更好的电化学性能；2)以Cu部分取代Fe,尽管会损失一定的电子电导率,但增加材料的离子电导率,使阴极的电催化性能提高,表明在阴极反应过程中离子电导率的增加对阴极反应具有重要的作用；3)具有抗Cr中毒性能的阴极接触材料Ni0.7Co0.3O(NC3O)可被直接发展成为阴极材料,以BZCYYb为电解质的电池在700℃时最大输出功率为204mWcm-2。第三章：针对中低温电解质掺杂Ce02在操作条件下存在一定的电子电导现象,提出一种低成本易实现的原位电子阻隔层制备技术。利用阳极中的Ba源在电池高温烧结成型过程中向铈基电解质层扩散的现象,在电解质/阳极界面处原位反应生成电子阻挡层,从而避免电池的内短路,提高电池的开路电压和燃料利用率。进一步研究发现NiO-BaZr0.1Ce0.7Y0.2O3-δ(NiO-BZC Y)对以La2Ce2O7(LCO)电解质的载流子具有一定的影响。形成的BaCeO3基反应层能提高电解质LCO的质子迁移数,使电解质更趋向于质子电导(其电解质的电导活化能为52.51kJmo1-1)；而以NiO-LCO为阳极的单电池电解质LCO以传导氧离子为主(电解质的电导活化能为95.08kJmo1-1)。第四章：传统Ni基阳极直接以碳氢化合物为燃料时易在Ni表面积碳,造成阳极催化活性和机械性能迅速下降,电池系统崩溃。为此,本章设计一种新型抗积碳阳极材料NiTiO3(NTO),该材料可在电池测试过程中NTO原位还原生成Ni-TiO2网状结构。700℃下,以NTO为阳极,SDC为电解质的单电池在甲烷为燃料时具有优异的抗积碳性能,40h几乎没有衰减,表明还原生成的网状连续结构的Ni-TiO2阳极具有很好的抗积碳性能。通过引入NTO-SDC阳极过渡层进一步优化电池结构,单电池在甲烷燃料下具有优异的电化学性能,最大功率密度达到0.413Wcm-2(700℃),其欧姆阻抗Rb和极化阻抗Rp分别为0.176和0.064Ωcm2。研究结果表明NTO是一种优异的低成本的抗积碳阳极材料。第五章：固体氧化物电解池(SOEC)是SOFC的电化学逆过程应用,可用于电网的峰谷调控。根据SOEC中Ni基电极在高温电解过程中出现的问题,本章中提出以钙钛矿型Sr0.95Y0.5TiO3+δ-Sm0.2Ce0.8O1.9直接作为电解池阴极,在SOFC和SOEC下进行对比研究。研究发现：1)XRD精修和电子顺谱共振(EPR)研究结果表明还原后Sr0.95Y0.5TiO3(SYT)结构中具有Ti3+离子的存在；2)SOEC模式下的总电阻均要小于SOFC模式下的总电阻,在SOEC模式下随着加载电压的增加,电池的欧姆电阻略有减小,而极化电阻大幅降低,表明加载电压的增加,有助于改善还原气氛下的SYT的电导率和催化活性。更多还原

【Abstract】 Energy crisis and environmental issues have become two major challenges for the sustainable development of human society. Solid oxide fuel cells (SOFCs) are a kind of clean and highly-efficient energy conversion device that converts the chemical energy in fuels directly to electricity with negligible emissions. To meet the commercialization requirement on cost and reliability, the operating temperatures of SOFC has to be lowered from traditional800-1000℃to intermediate and low-temperatures ranging400-800℃. Unfortunately, the lowered operating tempreture bring forth new challenges to SOFCs, including1) much lowered electro-activity of tranditional cathodes, which depress the discharging output of SOFCs;2) the electronic conduction in doped ceria, which the most promising intermediate-temperature electrolyte materials, decreased the open circuit voltage of cell and thus energy conversion efficiency;3) the carbon depositing on tranditional Ni anode when directly using hydrocarbon fuels, which greatly shorten the lifetime of SOFCs.Aimed to develop IT-SOFCs, several topics are involeved in this thesis, including:1) exploring suitable intermediate temperature cathode materials based on the investigation of electrode reaction mechanism;2) developing in-situ reaction layer to block the electronic conduction in doped ceria electrolyte;3) exploring novel carbon-tolerant anode materials that can be used directly in hydrocarbons fuels. The main results are shown as follows:Chaper1:A brief introduction of the research background, the basic working principle as well as general research progress of SOFC. Major challenges in key materials for low-temperature SOFC are also addressed. Based on these analysises, the main topics of this thesis are issued.Chapter2; To improve the electro-activity of cathode at intermediate temperature, several new cathode materials are explored and applicated, including double perovsikite-type LaBaCuCoO5+x (LBCC) and LaBaCuFeO5+x (LBCF), Sm0.5Sr0.5Fe0.8Cu0.2O3-δ (SSFCu), SrFe0.9Sb0.1O3-δ(SFSb) and Ni0.7Co0.3O (NC3O). Investigations on these new cathode materials suggest:1) Co doped LaBaCuO5+x has better electrochemical activity than Fe doped one;2) Copper substitution in SSFCu improved its oxygen ionic conductivity at the cost of electronic conductivity. The improved ionic conductivity benefits the cathode reaction process;3) Cr-tolerant Ni0.7Co0.3O can be directly used as the cathode material. A maximum power densities of204mW cm2with the electrolyte BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) was achieved at700℃.Chapter3:An easy in situ electronic-blocking reaction layer fabrication technique is proposed to slove the electronic conduction in doped ceria electrolyte. A NiO-BaZr0.1Ce0.7Y0.2O3-δ (NiO-BZCY) composite was proposed as the anode substrate for doped ceria electrolyte. During the co-sintering process of anode and electrolyte, Ba partially migrates from anode to electrolyte and formed a thin electronic-blocking layer for doped ceria. Intensive study also suggested that the formed BaCeO3-based reaction layer could largely improve the proton transferring number of La2Ce2O7(LCO). The activation energy of the LCO electrolyte conductivity differed with anode materials, approximately52.51kJ mol"1with NiO-BZCY anode and95.08kJ mol-1with NiO-LCO anode, respectively.Chapter4:A low cost carbon-tolerant anode material NiTiO3(NTO), which is reduced to Ni/TiO2with nano-network structure in reducing atmosphere, is designed and applied for SOFCs using hydrocarbon fuels. Within the tested40h’s long time test in humidied methane fuel, no decay in discharging performance was found, suggesting that NTO is a good carbon-tolerant anode. By introducing NTO-SDC active layer, the maximum power output of the cell with NTO-10%SDC/NTO-SDC/SDC/LSCF-SDC structure is413mWcm-2at700℃with humidified CH4(～3%H2O) as fuel. Low ohmic resistance and polarization resistance of0.176Ω2cm2and0.064flcm, respectively, are achieved, suggesting that NTO has good electrochemical activity to anode reaction.Chapter5:Solid oxide electrolysis cell (SOEC) is the reverse reaction system of SOFCs, and could be used to adjust the peak shaving of power grid along with SOFCs. In this work, Sr0.95Y0.5TiO3+δ was used as Ni substitute in SOECs to improve the cell performance. The XRD Rietveld refinement and electron paramagnetic resonance investigation suggests that Sr0.95Y0.5TiO3+δ powders reduced in H2has high-spin Ti3+with unpaired electron. Impedance study of a cell with SYT-SDC/YSZ/LSM-YSZ structure show that the polarization resistance in SOEC mode is much lower that that in SOFC mode, suggesting that the applied voltages help to improve the electrical conductivity and catalytic activity of SYT under a reducing atmosphere.更多还原