【作者】 张勇；

【导师】 梁叔全； 肖平；

【作者基本信息】 中南大学 ， 材料科学与工程， 2012， 博士

【摘要】 在传统能源供应日趋紧张,生态环境日益恶化的情况下,新型环保、安全、高效的燃料电池越来越广泛地受到人们的青睐与关注。但迄今为止,燃料电池在走向实际应用的道路上仍面临着技术及成本等众多不容忽视的问题,严重制约着燃料电池产业的进一步发展。在燃料电池开发过程中,新型电池材料及其制备技术的开发与应用,直接影响着燃料电池运行的效率及成本,是发展燃料电池技术的核心和基础。本论文以新型燃料电池——碱性铝燃料电池和固体氧化物燃料电池为研究背景,重点开展了有关碱性铝燃料电池电解液缓蚀剂、碱性铝燃料电池铝合金阳极以及固体氧化物燃料电池合金连接体保护涂层制备和表征的相关研究,目的在于通过开发新型电池材料及其制备技术,进一步提高电池效率,降低电池成本,推进燃料电池技术的进步。在缓蚀剂研究方面,系统研究了氢氧化铟、锡酸钠、柠檬酸钠以及间苯二酚对铝合金阳极在85℃,Smol·L-1/NaOH电解液中以800mA·cm-2的大电流密度放电时腐蚀行为以及电化学行为的影响,并在此基础上合成了能同时发挥各组分特长,综合应用性能优良的MCI (modified compound inhibitor)复合缓蚀剂。在铝合金阳极研究方面,以添加适量MCI改性复合缓蚀剂的5ml·L-1NaOH溶液为电解液,系统研究了合金元素、固溶热处理制度以及热轧工艺对铝合金阳极在85℃,含MCI的Smol·L-1NaOH电解液中以800mA·cm-2的大电流密度放电时的耐腐蚀性能以及电化学性能的影响,并系统分析了合金元素以及热处理轧制工艺在铝合金阳极组织以及性能变化过程中的作用机制。在合金连接体保护涂层研究方面,分别采用溶胶-凝胶(sol-gel)和电泳沉积(EPD)方法在Crofer22APU合金连接体表面制备了Cu-Mn (Cu1.2Mn1.8O4)以及Mn-Co (Mn1.5Co1.5O4)尖晶石保护涂层,系统研究了沉积工艺以及烧结制度对涂层保护Crofer22APU合金在800℃高温氧化120h前后组织结构的影响,同时对涂层保护合金连接体在高温长时间氧化过程中的氧化动力学行为及导电性能进行了评估。通过以上研究,获得了以下重要结论：1.某单位碱性铝燃料电池所用特种铝合金阳极材料在85℃、5mol·L-1NaOH电解液中以800mA·cm-2的大电流密度放电时电极电位较负,电化学活性较好,但其在高温强碱性电解液中的耐蚀性能较差,析氢腐蚀速率高达0.906mL·min-1·cm-2,因而在高温强碱性电解液中使用时需要添加相应的电解液缓蚀剂；2.对单一缓蚀剂的研究表明,In(OH)3是综合性能较好的单组份缓蚀剂,当其浓度为4mmol·L-1时,铝合金阳极材料的析氢速率为0.295mL·min-1·cm-2,电极电位为-1.597V。Na2SnO3是对铝合金阳极具有最好抑氢作用的单组份缓蚀剂,缓蚀剂缓蚀效率高达81.29%,但Na2SnO3的加入会对铝合金阳极电化学活性的发挥产生较大影响。柠檬酸钠是对铝合金阳极电化学活性影响最小的单组份缓蚀剂,而与柠檬酸钠正好相反,间苯二酚是对铝合金阳极电化学活性影响最大的单组份缓蚀剂；3.所研发的改性复合缓蚀剂MCI有力发挥了无机有机缓蚀剂之间的协同缓蚀效应,当在电解液中加入适量的MCI后,铝合金阳极析氢速率仅为0.134mL·min-1·cm-2,缓蚀剂缓蚀效率高达86.65%,而此时铝合金阳极的电极电位仍然较负,为-1.589V,说明MCI在保证铝阳极良好耐蚀性能的同时,又能使铝阳极具有较好的电化学活性。同时所开发的MCI改性复合缓蚀剂同各单组份缓蚀剂都是通过抑制阳极反应来减缓析氢腐蚀速率,同属于阳极抑制型缓蚀剂；4.对碱性铝燃料电池新型铝合金阳极材料的开发研究表明,适当含量的高析氢过电位元素Sn和In在合金中的加入既可以提高铝阳极材料的耐腐蚀性能,又可以分别通过降低阳极氧化膜离子阻力和在基体中形成低共熔体合金来减小阳极极化,提高材料电化学活性。元素Ga虽然也可以在一定程度上提高铝阳极电化学活性,但含量较高时,铝阳极析氢腐蚀严重,耐蚀性能较差。混合稀土元素主要通过提高合金组织均匀性,减小活性偏析相聚集来同时提高铝阳极耐腐蚀性能和电化学活性；5.固溶热处理制度对新型铝合金阳极材料耐腐蚀性能和电化学性能的影响主要是通过提高合金元素固溶度,减少活性元素偏析团聚来实现的,轧制工艺对铝合金阳极材料耐腐蚀性能和电化学性能的影响主要是通过动态再结晶来实现的。研究表明,当对540℃下固溶处理5h后的新型铝合金材料在420℃,以40%的道次变形量进行轧制时,合金组织中动态再结晶过程得以进行,基体中活性元素大量固溶且分布均匀,偏析相团聚现象减少,此时,铝合金阳极材料不仅具有最小的析氢腐蚀速率(0.089mL·min-1·cm-2),而且具有最负的电极电位(-1.630V),材料耐腐蚀性能和电化学活性最好；6.通过电泳沉积(EPD)方法在合金连接体表面制备Mn-Co尖晶石保护涂层是提高合金连接体材料综合应用性能的有效表面改性方法。所制备的Mn1.5Co1.5O4尖晶石保护涂层,不仅可以有效提高合金连接体材料在高温长时间氧化过程中的抗氧化性能,减缓Cr2O3氧化层厚度的进一步增长,同时还能有效阻止元素Cr在涂层中的挥发与扩散,从而减少阴极材料“铬中毒”现象的发生；7.通过合适烧结工艺(1100℃氩气气氛烧结)既可以保证烧结过程中在涂层(2.3μm)和基体间所形成的Cr2O3氧化层厚度较薄,Crofer22APU合金连接体高温氧化过程中的稳定ASR值(13.1mΩ·cm2)较小,同时可以保证所制备的Mn-Co尖晶石保护涂层结构致密,合金连接体在高温长时间氧化过程中氧化速率(6.31×10-15g2·cm-4·s-1)较低。更多还原

【Abstract】 The newly developed fuel cells with high efficiency, low pollution and reliable safety have been paid more and more attention recently due to the shortage of traditional energy and deterioration of environment. However, problems such as technology and cost in the practical application of fuel cells still restrict the further development of fuel cell industry. In the research process of fuel cells, the development and application of new battery materials and their manufacturing process, which determines the efficiency and cost of the cell operation, are the core and foundation of fuel cell technology. Taking alkaline aluminum fuel cells and solid oxide fuel cells as the background, this dissertation mainly focuses on the research in preparation and characterization of inhibitors and aluminum alloy anodes in alkaline aluminum fuel cells as well as the protective coatings of metal interconnect in solid oxide fuel cells (SOFCs). All the work is aimed to improve the cell efficiency, reduce the cost and promote the progress of fuel cell industry by developing new battery materials.In term of inhibitors, effect of In(OH)3, NaSnO3, sodium citrate and resorcinol on the corrosion and electrochemical behaviors of aluminum anode in85℃, Smol·L-1NaOH electrolyte with current density of800mA·cm-2has been studied respectively. Based on the research of single inhibitors above, a modified composite inhibitor (MCI) which can help the aluminum anode to gain a well balance between corrosion resistance and electrochemical activity has been newly developed. With regard to the research of aluminum alloy anodes, effect of alloy elements, solution heat treatment and hot rolling process on the corrosion and electrochemical behaviors of aluminum anode in85℃, Smol·L-1NaOH electrolyte (containing MCI inhibitor) with current density of800mA·cm-2has been investigated comprehensively. The effect mechanism of alloy elements, heat treatment and rolling process on the micro structure and performance of aluminum alloy has been analyzed as well. In research of interconnect protective coatings, the Cu-Mn (Cu1.2Mn1.8O4) and Mn-Co (Mn1.5Co1.5O4) spinel protective coatings have been prepared on the surface of Crofer22APU stainless steel using sol-gel dip coating and electrophoretic deposition method respectively. The effect of deposition technique and sintering process on the microstructure of coated Crofer22APU alloy before and after oxidizing at800℃for up to120h has been studied. The oxidation kinetics behavior and electrical property of coated substrate during oxidation are also evaluated. The main results obtained are described as follows:1. The selected aluminum alloy anode owns the excellent electrochemical activity with negative electrode potential in85℃, Smol·L-1NaOH electrolyte with current density of800mA·cm-2. But the hydrogen evolution corrosion of the alloy in high temperature and strong alkaline electrolyte is really serious and the hydrogen evolution rate is high at0.906mL·min-1·cm-2. The aluminum alloy anode is not suitable for use in pure alkaline electrolyte and needs the assistance of inhibitor;2. The study of single inhibitors shows that In(OH)3is the best single inhibitor with favorable electrochemical comprehensive performance. When the concentration of In(OH)3is4mmol·L-1, the hydrogen evolution rate of aluminum anode is0.295mL·min-1·cm-2and the electrode potential is-1.597V. Na2SnO3is the best single inhibitor in decreasing the hydrogen evolution corrosion of the aluminum anode, however, the addition of Na2Sn03will have negative effect on the electrochemical activity of aluminum alloy anode. Sodium citrate owns the minimal impact on the electrochemical activity of aluminum alloy anode. By contrast, resorcinol has the great impact on the electrochemical activity of aluminum alloy anode;3. The modified composite inhibitor (MCI) plays a synergies effect between inorganic and organic inhibitor fiercely. With the addition of MCI, the hydrogen evolution rate of aluminum anode decreases to its lowest value at0.134mL·min-1·cm-2and the inhibition efficiency of inhibitor increases to the highest value at86.65%. Meanwhile, the electrode potential of aluminum anode is still negative at-1.589V, which reveals that MCI can help the aluminum alloy anode to gain a well balance between corrosion resistance and electrochemical activity in alkaline electrolyte perfectly. In addition, both the MCI inhibitor and the single inhibitors mentioned above are all belongs to the anode-restrained inhibitor which slows down the hydrogen evolution corrosion by restraining the anode reaction;4. The study of novel aluminum alloy anode shows that addition of high hydrogen overpotential elements Sn and In in aluminum alloy will not only enhance the corrosion resistance of alloy, but also can decrease the anodic polarization and improve the electrochemical activity of aluminum anode by reducing the ion resistance of anodic oxide films and forming low melting point alloys respectively. The addition of Ga can also improve the electrochemical activity of aluminum anode to some extent, but high content of Ga will reduce the corrosion resistance of aluminum anode. The mixed rare earth elements can enhance both the corrosion resistance and electrochemical activity of aluminum alloy anode by improving the uniformity of the microstructure;5. The electrochemical comprehensive performance of aluminum alloy anode can be improved by the solution heat treatment which can increase the solid solubility of alloy elements and decrease the aggregation of active segregation phases. The effect of rolling process on the corrosion resistance and electrochemical activity of aluminum alloy anode is achieved by the dynamic recrystallized. The uniform microstructure with homogeneous distribution of fine active segregation phases as well as the excellent electrochemical comprehensive performance of newly development aluminum alloy anode is achieved by the dynamic recrystallization under420℃with pass deformation of40%after taking heat treatment at540℃for up to5h. The optimized aluminum alloy anode has the lowest hydrogen evolution rate of0.089mL·min-1·cm-2and the most negative electrode potential of about-1.630V;6. The relatively dense, uniform and well adherent Mn1.5Co1.5O4spinel coating which could significantly improve the oxidation resistance of stainless steel substrate and effectively act as a mass barrier to the outward migration of chromium during long-term oxidation process is successfully prepared on the surface of Crofer22APU stainless steel substrate by electrophoretic deposition technique, which indicates that preparation of Mn-Co protective coatings by electrophoretic deposition technique is the effective surface modification method in improving comprehensive application performance of metal interconnects;7. The appropriate sintering process (1100℃in Ar atmosphere) of Mn-Co (2.3μm) coated Crofer22APU can not only make sure that a thin Cr2O3oxide layer and low ASR of13.1mΩ·cm2to be obtained, but also can help to form a dense Mn-Co coating layer and to get a low parabolic rate constant of6.31×10-15g2·cm-4·s-1.更多还原