【作者】 唐玉宝；

【导师】 刘江；

【作者基本信息】 华南理工大学 ， 应用化学， 2011， 博士

【摘要】 直接以碳为燃料的直接碳燃料电池（Direct Carbon Fuel Cell,DCFC）,理论转化效率高达100%以上,可使用经过简单加工处理的煤为燃料,为高效、清洁地使用煤提供了一种新途径。其中以固体氧化物为电解质的直接碳固体氧化物燃料电池（Direct Carbon Solid Oxide Fuel Cell,DC-SOFC）采用全固态结构,避免了使用液态电解质带来的腐蚀泄露问题,碳燃料潜在的电能达到⁹Ah/g,因此DC-SOFC可能成为一种高储能密度电池,具有可观的发展前景。目前,DC-SOFC的研究还处在实验室基础研究阶段。本论文采用注浆成型工艺制备了YSZ电解质管,在1600oC下烧结4h后,机械强度高,微观结构致密,达到了制备电池的要求。本论文设计了一种结构简单,容易制作,采用全固态结构的管式YSZ电解质支撑的DC-SOFC装置。采用纯石墨为燃料研究了电池的输出性能,结果表明设计的DC-SOFC具有可行性,但电池衰减严重。通过热力学平衡计算了过量的碳和氧气反应在各个温度下达到平衡时产物的成分,在温度>750oC时产物主要是CO气体,温度<750oC时产物主要是CO2气体,结合实验结果和理论计算分析了DC-SOFC的反应机理,阳极上CO的电化学氧化反应和碳燃料的Boudouard反应是其关键反应。本论文改变碳燃料,使用活性炭为燃料进行了电池输出性能、阻抗性能和稳定性的研究。结果表明电池的界面极化电阻在电池总耗损中占主导,没有使用任何流化气体电池稳定运行了37h,比石墨燃料稳定,证明了电池可以自维持工作。指出电池的性能和燃料自身的性质有关,阳极上CO的电化学氧化反应和碳燃料的Boudouard反应两反应的反应速率相协调,电池才能维持长久稳定运行。本论文在电池阳极和碳燃料中添加了GDC和Fe催化剂,研究了其对电池输出性能,阻抗性能和稳定性的影响,表征了电池的微观结构和碳燃料在电池反应前后的变化。结果表明添加的GDC改善了阳极结构,催化了阳极上CO的电化学氧化反应,减小了界面极化电阻,大大提高了电池的性能,Fe催化剂促进了碳燃料的Boudouard反应,使得碳燃料充分被消耗,添加的催化剂也提高了电池的稳定性。EDX表征表明电池反应后燃料残余物中含C极少,可以忽略。XRD表征表明燃料残余物主要是纳米级的Fe₂O₃。本论文针对Boudouard反应催化剂,研究了Fe催化剂和Ni催化剂的含量对Boudouard反应的影响。当Fe含量为5-7%和Ni含量为5%及以上时,对活性炭Boudouard反应的催化效果达到最好。本论文制备了分别以Ag-SDC和Ni-SDC为阳极的YSZ电解管支撑型SOFC,研究了它在干CO燃料下的输出性能、阻抗性能和稳定性。干CO燃料下,Ag-SDC阳极的性能大大优于Ni-SDC阳极的;Ag-SDC阳极稳定运行了95h其性能只下降了8.3%,而Ni-SDC阳极只运行了37h,性能下降了77.6%。SEM表征表明Ag-SDC阳极在稳定性测试后,Ag有轻微的烧结现象,Ni-SDC阳极在稳定性测试后,结构发生很大变化,Ni烧结严重。EDX分析结果表明Ag-SDC阳极表面碳沉积很少,可以忽略;而Ni-SDC阳极表面碳沉积很严重。更多还原

【Abstract】 Direct carbon fuel cell （DCFC）, which converts the chemical energy of carbon directly to electricity with a theoretical conversion efficiency a little bit over 100%, can use simply processed coal as fuel, provides a new way for using coal cleanly and efficiently. Direct carbon solid oxide fuel cell （DC-SOFC） is a whole-solid state device which has no problem of liquid corrosion and leakage. As carbon has a theoretical energy density of ⁹Ah/g, there is great potential to developt DC-SOFC into a high-performance battery. So DC-SOFC has a considerable development prospect. At present, the research of DC-SOFC is still in its early stage.In the work presented in this paper, YSZ electrolyte tubes have been prepared by slip casting. After sintered at 1600oC for 4h, they become dense and their mechanical strength is high. All these properties meet the requirements for preparing the SOFCs.In the present work, we have designed a YSZ electrolyte supporting tubular DC-SOFC device which has a simple and whole-solid-state structure. The output performance of the DC-SOFC using pure graphite as fuel has been researched. The results show that the designed DC-SOFC is feasible. However, the cell performance decayes seriously. The composition of the product produced by the reaction of sufficient carbon and O₂ has been calculated through the thermodynamic equilibrium theory. When the temperature is larger than 750oC, the produced gas is mainly CO, while when the temperature is smaller than 750oC, the produced gas is mainly CO₂. The reaction mechanism of DC-SOFC has been analysed through the experimental results and the theoretical calculation. It is pointed out that the electrochemical oxidation reaction of CO on the anode and the Boudouard reaction of carbon fuel are the key reactions in a DC-SOFC.In the present work, DC-SOFCs with activated carbon are prepared and their output performance, resistance and stability have been studied. The results show that the interfacial polarization resistance of the cell dominates the total loss in the cell. A 37h stable operation of a DC-SOFC with activated carbon has been realized, demonstrating that such DC-SOFCs can be self-sustaining. The cell performance is related to the nature of carbon fuel. It is suggested that the electrochemical oxidation reaction of CO on the anode and the Boudouard reaction of carbon fuel can maintain long-term stable operation as their reaction rates are coordinate.In the present work, GDC and Fe catalysts have been added to the anode and carbon fuel, respectively, and their influence on the cell output performance, impedance performance and stability have been studied. The change of the cell microstructure and carbon fuel micro-morphology before and after the cell reaction also has been characterized. The results show that the added GDC improves the anode structure and catalyses the electrochemical oxidation reaction of CO on the anode, and reduces the interfacial polarization resistance, so that the cell performance is greatly improved. Fe catalyst catalyses the Boudouard reaction of carbon fuel and makes the carbon fuel fully consumed. The stability of the cell is also improved by the added catalysts. EDX analysis shows that after the cell reaction, the fuel residue contains very little carbon that can be ignored. XRD analysis shows that the fuel residue is mainly nanoscale Fe₂O₃.In this paper, the influence of the content of Fe and Ni catalysts on the Boudouard reaction has been studied. When the content of Fe is 5-7% and Ni is of 5% or more, the catalytic effect is the best.In the present work, YSZ electrolyte supporting tubular SOFCs with Ag-SDC and Ni-SDC anode, respectively, have been prepared. The output performance, the impedance performance and stability operated on CO fuel have been studied. Performance of Ag-SDC anode is much better than that of Ni-SDC anode on dry CO fuel. After stable operation of a 95h, the performance of Ag-SDC anode declined only 8.3%, while the performance of Ni-SDC anode declined 77.6%, after stable operation of a 37h. SEM characterization shows that Ag is slightly sintered after the stability test of Ag-SDC anode, while the Ni-SDC anode structure changes considerably and Ni is sintered seriously. EDX and XRD analysis show that carbon deposition on Ag-SDC anode surface is rare that can be ignored, while carbon deposition on Ni-SDC anode surface is very serious.更多还原