【作者】 陶泽天；

【导师】 刘卫；

【作者基本信息】 中国科学技术大学 ， 材料学， 2011， 博士

【摘要】 由于能源危机以及环境污染等问题已经成为人类生存及发展的主要威胁，开发和使用经济洁净的新能源成为人们面临的重大挑战之一。固体氧化物燃料电池由于具有清洁，环境友好等诸多优点而受到世界范围的广泛关注，各主要国家还纷纷投入大量财力、物力、人力开发研究。然而，传统的固体氧化物燃料电池操作温度较高，对于电池材料要求苛刻，导致电池系统成本过高，因此如何降低电池的操作温度成为燃料电池能否商业应用的一个迫切需求。其中，固体氧化物质子导体固体氧化物燃料电池以其较低的活化能以及高的能源效率成为研究的热点。本论文主要针对质子导体固体氧化物燃料电池传统电解质材料BaCeO₃存在的一些问题，试图通过探索研究新型的电解质以及阴极材料予以解决。论文的第一章，简单介绍了燃料电池的工作原理以及各组成部分，并针对固体氧化物质子导体燃料电池的电解质材料以及阴极材料的发展进行了阐述，同时提出了质子导体燃料电池中存在的一些函待解决的问题。在第二章中，我们利用一种浆料浸渍制备质子导体电解质的方法，成功的在NiO-BaZr_0.1Ce_0.7Y_0.2O_3-δ) （BYCZ）衬底上制备了一层BYCZ薄膜。我们主要研究了这一过程中某些重要常数对于电池测试结果的影响，比如浆料中BYCZ的含量以及衬底的预烧温度。研究的结果表明，浆料中固含量为5%，衬底预烧温度500 C时，我们制备的电池具有较好的电化学表现。第三章我们针对BaCeO₃质子导体体系存在的稳定性问题，提出了利用Ga掺杂来改善BaCeO₃的稳定性，得到BaCe_1-xGa_xO_3-δ（x=0.1, 0.2）系列材料。通过热重分析以及XRD表征，我们发现，Ga掺杂体系具有较好的化学稳定性。结合喷雾的方法，成功的制备出具有BaCe_0.8Ga_0.2O_3-δ电解质的质子电池，电池在600°C具有较好的长期稳定性，而且得到了较好的功率密度，表明Ga是一种较为合适的掺杂元素。第四章里，我们尝试用一种新型的质子导体电解质材料La_1.95Ca_0.05C_e2O_7-δ（LCCO）制备电池。我们首先评价了LCCO的粉体的化学稳定性：在700°C，3%CO₂气氛下处理粉体100小时，材料相结构没有变化，保持萤石结构；而在沸水中处理100小时后粉体相组成也没有发生变化。这些结果表明我们制备的LCCO粉体具有高度的化学稳定性。另外，我们利用喷雾的方法成功地在LCCO-NiO的阳极衬底上制备出15um左右的电解质薄膜。电化学测试结果表明，由于Ce元素的变价，电池的开路电压在700°C时只有0.832V，单电池功率密度与传统电解质电池相比稍低。但考虑到LCCO展现出的在严苛电池测试条件下展现出的高度稳定性，及可通过增加一层高开路电压的电解质阻隔层的措施来提高LCCO电池性能，因而LCCO还是有望成为一种具有应用价值的电池电解质。第五章我们对具有质子导电性的La₂Z_r2_O7体系中Ca²⁺掺杂含量进行了计算研究。在本章里，我们利用XRD检测并结合计算机模拟的方法，确认了La₂Zr_2O7中Ca²⁺最大掺杂含量为0.08，同时利用质子电导率的检测来证实我们的结论。由于La₂Zr_2O7具有高度的化学稳定性，可以在较为苛刻的环境中稳定存在，是一种颇为有潜力的质子电解质材料，我们的工作为La2Zr2O7未来的可能应用打下了一定的基础。第六章里，与传统复合阴极材料不同，我们采用BaCeO₃结构的BaCe_0.5Bi_0.5O_3-δ（BCB）作为单相阴极材料。并据此，我们提出了一种全新的三相界面的观念，指出具有质子，电子以及氧离子导电的材料具有最大的活性区域。我们在加入功能层材料的NiO–BZCY7/BZCY7单电池上检测这种单相阴极材料的电化学性能，最大功率密度已经可以达到321mW/cm²，与使用传统的阴极材料的电池性能相差无几。值得指出的是：由于BCB材料本身与电解质材料结构相近，两者之间的化学兼容性以及热匹配都非常好。这种新型结构的阴极材料为我们以后质子导体燃料电池的阴极选择提供了一种全新的途径。为了解决上面BCB阴极存在的电导率还不足够高的问题，在第七章我们深入研究了Fe掺杂的BaCeO₃材料，即BaCe_xFe_1-xO_3-δ（x=0.15, 0.50, 0.85）。利用XRD检测三者的相结构，我们发现BCF1585是立方钙钛矿结构，BCF8515属于正交晶系，而BCF5050相当于两者混合物。在NiO–BZCY7/BZCY7半电池上面，我们检测了三种阴极材料的电化学表现，我们发现BCF5050在700oC不仅具有最低的极化电阻0.17Ωcm²，而且可以获得最高的功率密度，可以达到395mW/cm²。由于BCF5050与电解质材料结构相近，它与电解质的化学兼容以及热匹配性较好，此外，由于BCF5050不含传统阴极材料中的Co元素，可以避免Co阴极存在的挥发性高以及热膨胀系数不匹配等问题，综上几点，我们认为BCF5050可以成为质子导体燃料电池的一种较为有潜力和应用价值的阴极材料。第八章我们对论文的主要内容进行了总结，对质子导体固体氧化物燃料电池以后的工作进行了展望。更多还原

【Abstract】 As the energy crisis and environment pollutions have been the main threaten forthe survival and development of people, the demands of clean and economical energybecome one of the most important challenges. Solid oxide fuel cells （SOFCs） haveattracted much attention worldwide because of the demand for clean, secure, andrenewable energy. However, the cost of SOFCs system is too expensive to use whenused at high temperature. The reduction of the working temperature of SOFCsbecomes the urgent demand for broad commercialization. The proton-conductingSOFCs attract more attention for low activation energy and high energy efficiency.This thesis tries to study the novel electrolyte and cathode materials to solve thetroubles and problems existed in the proton-conducting SOFCs.Chapter 1 in the thesis simply describes the working principle and differentcompositions of the SOFCs. We mainly introduce the development of the electrolyteand cathode materials for Proton-conducting SOFCs. At the same time, we point outthe problems existed and try to search novel electrolyte and cathode materials to solvethe problems in the Proton-conducting SOFCs.In Chapter 2, we study a drop coating method to prepare the thin electrolytemembrane with high quality and successfully prepare a thin layer of BYCZ membraneon the anode substrate NiO-BaZr_0.1Ce_0.7Y_0.2O_3-δ（BYCZ）. We mainly study someconstants which may affect the cell performance, such as solid contents of BYCZ andpre-fired temperatures of anode substrates. The electrical results and SEM indicatethat the right content of BYCZ in the drop-coating slurry is 5wt. % and theappropriate pre-fired temperature is 500°C.In Chapter 3, in order to solve the chemical instability of BaCeO₃, we successfulsynthesized BaCe_1-xGa_xO_3-δ（x=0.1, 0.2） by a solid-state reaction method. Thecompounds containing Ga showed desired chemical stability in3% CO₂duringthermal gravity analysis test from 400 to700°C. With a wet suspension approach toprepare the electrolyte of BaCe_0.8Ga_0.2O_3-δ(,a single cell is assembled and tested. Theshort-term performance test at 600°C demonstrates that the fuel cell has good stabilityas well as desired compatibility between electrolyte and electrodes. Therefore, thedoping of Ga in BaCeO₃provided an effective strategy comprising high protonconductivity and adequate chemical stability for BaCeO₃-based materials.In Chapter 4, a novel electrolyte material La_1.95Ca_0.05Ce₂O_7-δ（LCCO）is studied.The stability of the synthesized powders is investigated under the CO₂atmosphere at 700oC and the boiling water with the X-ray diffraction （XRD）. According the resultof XRD, the material is very stable and with no reaction with CO₂and H₂O. A fuelcell with electrolyte of La_1.95Ca_0.05Ce₂O₇-（?）is prepared by a suspension spray andtested. The open-circuit potential is only 0.832V at 700°C and the electronicconductivity arose by the reduction Ce⁴⁺to Ce³⁺is the main reason. The maximumpower density is a little lower than the cell with tradition electrolyte. The highchemical stability and the possibility to increase open-circuit potential by bi-layerelectrolyte both make the material be a potential commercial useful electrolyte inSOFCs.In Chapter 5，a simple and available method based on the XRD intensity ratioand computer simulation is employed to determine the Ca-doping content inpyrochlore-structured La_2-xCa_xZr₂O_7±δ. XRD analysis shows that the highestCa-doping content is 0.08. The measurement of electrical conductivity reveal that thelargest conductivity is got at x=0.08. Both the XRD intensity ratio analysis and theelectrical measurement confirm that the maximum Ca-doping content at La site is0.08. La₂Zr₂O₇is a very potential electrolyte for its high chemical stability. Our workshave greatly promoted the use of this novel material.In Chapter 6, we prepare the BaCe_0.5Bi_0.5O_3-δ（BCB）and use it as the singlephase cathode material which is different from traditional composite cathodematerials. We also employ a new principle of Three Phase Boundary （TPB） whereallows the simultaneous transport of proton, oxygen vacancy, and electronic defects,which effectively extend the active‘‘sites for oxygen reduction to a large extent andreduce the cathode polarization resistance. Without an addition of the electrolytepowder for the cathode, the single cell NiO–BZCY7/BZCY7/BCB generated amaximum power density of 321mWcm^-2 at 700°C, which can compare with theproton-conducting SOFCs with composite cathode materials. More important, theBCB was a protonic material with the substitution of Bi for Ce in the BaCeO₃, whichcan be chemically and thermally compatible to the BaCeO3-based electrolyte for theproton-conducting SOFCs. These results indicated that the cathode BCB was a goodcathode material candidate for proton-conducting SOFCs operating at or below 700°C.In order to solve the problem of low conductivity of BCB in Chapter 6, we studythe BaCe_xFe_1-xO_3-δ（x=0.15, 0.50, 0.85） in Chapter 7. According to the XRD,BCF1585 has a cubic perovskite structure and BCF8515 belongs to the orthorhombic structure. As for BaCe_0.5Fe_0.5O_3-δ（BCF5050）, it is found that the sample comprisestwo kinds of perovskite oxides mentioned above. The cell with cathode BCF5050shows the highest performance which can reach a relatively high power density of395 cm^-2at 700°C. Under the open-circuit condition, the polarization resistance of theelectrode is as low as 0.17Ωcm2at 700°C. BCF5050 can be chemically andthermally compatible to the BaCeO₃-based electrolyte for the proton-conductingSOFCs. Furthermore, cobalt-free BCF5050 can avoid many problems of the traditioncathode materials based on cobalt doping, such as high thermal expansion coefficients（TECs） and high volatility of cobalt element. These results indicate that the cathodeBCF5050 was a good cathode material candidate for proton-conductingSOFCsFurthermore.In Chapter 8, the achievements presented in this dissertation areevaluated and future work concerning the development of proton-conducting SOFCsis discussed.更多还原