【作者】 王涛；

【导师】 何建平；

【作者基本信息】 南京航空航天大学 ， 材料物理与化学， 2012， 博士

【摘要】 金属双极板作为燃料电池的关键部件，在燃料电池工作过程中因电化学腐蚀，表面腐蚀产物不断增厚，使双板板的接触电阻增大，导致部分电能转换为热能，从而降低燃料电池能量转换的效率。通常在金属双极板表面涂覆一层导电防护膜，来解决或最小化上述问题的影响。本论文首次尝试将有序介孔碳制成薄膜应用于质子交换膜燃料电池不锈钢双极板表面防护，提出薄膜成分选择的新思路，通过在纳米尺度上进行多组分的协同组装对介孔碳膜进行改性，探讨薄膜微观结构形成机制，在模拟质子交换膜燃料电池酸性溶液中研究有序介孔碳基薄膜的电化学特性。论文的主要内容介绍如下：1、结合溶剂挥发诱导自组装法和旋涂法，以嵌段共聚物F127为模板剂，酚醛树脂为碳源，在304不锈钢表面直接制备有序介孔碳膜。结构测试显示，有序介孔碳膜的比表面积在500⁶50m2g^-1，孔容0.4⁰.5cm³g^-1，介孔比例大于70%，说明其具有较好的介孔结构。相比于不锈钢裸片，涂覆有序介孔碳膜后，腐蚀电位提高了100⁴00mV，腐蚀电流下降了1个数量级，模拟质子交换膜燃料电池的恒电位极化时，腐蚀电流密度可低至0.464μA cm^-2，但此时接触角仅为71°，电导率为0.0043S m^-1。进一步提高热处理温度，会引起骨架的收缩，介孔碳膜局部产生裂痕，在极化测试过程中极不稳定，导致电荷传递阻抗的降低和腐蚀产物扩散速率加快。针对纯介孔碳膜的缺点，我们尝试了下面4种改性途经。2、在有序介孔碳膜中引入刚性的二氧化硅组分，强化介孔碳膜的热稳定性和防腐性能。通过三元共组装制备介孔碳-二氧化硅复合膜，在400到700℃的热处理过程中，其孔径收缩了12.2%，较纯介孔碳收缩14.7%，明显降低，扫描电镜测试显示复合膜表面未见裂痕。电化学测试表明，经二氧化硅复合后的有序介孔碳膜腐蚀电流密度(0.0975μAcm^-2)减小为纯介孔碳膜的五分之一，碳化温度达700℃时恒电位极化曲线也非常稳定，说明高温热处理后碳-二氧化硅薄膜的致密性依然较好。3、在介孔碳中分别掺杂B、P、N等元素形成杂化介孔碳，以改善介孔碳的石墨化程度和防腐性能。在高温热处理时，这些元素有利于酚醛树脂由无定形向石墨化转变，提高了涂层的导电能力和疏水性，其中硼酸的加入还能一定程度上提高了薄膜的热稳定性。如热处理温度为500℃时，掺杂B、P、N的介孔碳膜电导率分别可达0.15、0.21、0.029S m^-1，对应的接触角分别为86、91、80°，显著高于纯介孔碳膜。恒电位极化测试显示，杂化介孔碳膜在0.5M H2SO4中具有良好的稳定性，动电位极化测试其腐蚀电流密度分别为0.285、0.0299、0.166μA cm^-2，表现出较好的防腐性能。4、将含W或Mo元素的前驱体添加于酚醛树脂前驱体中，分别制备有序介孔碳-钨复合薄膜和碳-钼复合薄膜。由于钨和钼化合物具有催化石墨化效应，介孔碳膜的石墨化程度和电导率随着这两种元素的含量的提高而增大。热处理温度为500℃时，其电导率分别可达0.82和0.11S m^-1。介孔骨架的特殊空间结构，引导钨化合物以规则的棒状形式生长，该棒状物主要由氧化钨和碳化钨组成。动电位极化测试结果显示碳-钨复合薄膜最低的腐蚀电流密度为0.0559μAcm^-2。有序介孔碳-钼薄膜具有非常致密的结构，钼主要以氧化钼和碳化钼的复合形式均匀的嵌入在碳壁中，粒径约4nm，在0.5M H₂SO₄中的自腐蚀电位为277mV，腐蚀电流密度仅有0.0273μAcm^-2。5、为了同时增强介孔碳膜的疏水性和电导率，在制备有序介孔碳的过程中原位加入高石墨化、高导电的石墨烯或碳纳米管，获得了高电导率、且具有微纳米粗糙结构的复合膜。其电导率分别0.35和0.41S m^-1，接触角为90和96°，在模拟PEMFC工作环境下的测试的自腐蚀电流密度分别为0.140和0.008μAcm^-2，表现出优异的防腐性能。更多还原

【Abstract】 Metal bipolar plates develop a passivating oxide layer on the surface that does protect the bulkmetal from progression of corrosion, but also cause an undesirable effect of a high surface contactresistance, especially as the passivating oxide layer is thickened during operation. This causes thedissipation of some electric energy into heat and a reduction in the overall efficiency of the fuel cellpower stack. The problems outlined above may be overcome or minimized by protecting metalbipolar plates from the corrosive fuel cell operating conditions with coatings which should beconductive and adhere to the base metal without exposing the substrate to corrosive media. In thispaper, ordered mesoporous carbon films are first used as protective coating of stainless steel bipolarplates. Ordered mesoporous carbon films are modified by cooperative assembly with othercomponents in nanometer scale. We discuss the formation mechanism of microstructures of compositefilms, put forward a new idea to select an appropriate component as modifier, and analyse theprotective properties against corrosion with samples exposed to sulfuric acid solution to simulateproton exchange membrane fuel cells environment. The main contents are as follows:1. Ordered mesoporous carbon film is prepared on the304stainless steel by the combination ofsolvent evaporation induced self assembly method and spin-coating method, with block copolymerF127as template agent, phenolic resin as carbon source. Structure tests display, ordered mesoporouscarbon films have a high specific area of500⁶50m2g^-1, pore volume of0.4⁰.5cm³g^-1, pore ratioof greater than70%. Compared with304stainless steel, ordered mesoporous carbon film makescorrosion potential shifted to positive direction by100⁴00mV, corrosion current decreased by1order of magnitude, potentiostatic polarization process in the operation pressure of a fuel cell is stable.The corrosion current density can be as low as0.464μA cm^-2, but the contact angle is71°and theelectrical conductivity is0.0043S m^-1. As the heat treatment temperature further rises, the structure ofordered mesoporous carbon film would shrink and generate some cracks, which could lead to theunstabitily of the polarized process, and reduce the charge transfer impedance, speed the diffusion rateof corrosion product. In order to improve the properties of pure mesoporous carbon film, we try to usefour method to modify mesoporous carbon.2. The rigid silica is introduced in the ordered mesoporous carbon film to strengthen the thermalstability and corrosion resistance. The results show that the mesoporous carbon-silica composite filmhas a highly ordered2D hexangular mesoporous structure. From400to700℃, the bore diameter is contracted by12.2%, whereas the pure mesoporous carbon is contracted by14.7%. Scanning electronmicroscope test shows that there is not crack in the surface of composite film. Electrochemical testshows that, the mesoporous carbon-silica composite film has a corrosion current density (0.0975μAcm^-2), which is1/5of the pure mesoporous carbon film. After heat treatment of700℃, potentiostaticpolarization curve of composite film is also very stable, the results show that composite film still has adensity structure after heat treatment of high temperature.3. Ordered mesoporous hybrid carbon films are prepared by tri-assembly with B, P, Ncompounds as dopant source. During the course of high temperature heat treatment, these elements isin favor of transition of phenolic resin from amorphous state to graphite, and can improve theconductivity and hydrophobicity of mesoporous carbon film. Boracic acid also can improve thethermal stability of the film. For example, when heating temperature is500℃, the conductivity of B,P, N doped mesoporous carbon films can reach to0.15,0.21,0.029S m^-1, the contact angles are86,91,80°, respectively, which are significantly higher than that of pure mesoporous carbon film.Potentiostatic polarization test shows, hybrid mesoporous carbon film in0.5M H₂SO₄has a goodstability. Potentiodynamic polarization tests show that the corrosion current density is0.285,0.0299,0.166μA cm^-2, respectively, which means better anti-corrosion properties.4. Ordered mesoporous carbon-tungsten（molybdenum） composite films are prepared by mixingthe the precursor of W or Mo and phenolic resin. As a result of the catalytic graphitization effect oftungsten and molybdenum compounds, the degree of graphitization and conductivity of mesoporouscarbon film can increase with the content of the two element. When heating temperature is500℃,their conductivity reaches to0.82and0.11S m^-1, respectively. Due to the confinement effect ofmesoporous structure, tungsten compounds, composed of tungsten oxide and tungsten carbide, aregrowing into rodlike. Potentiodynamic polarization shows that the lowest corrosion current densityof the mesoporous carbon-tungsten composite film is0.0559μA cm^-2. Ordered mesoporouscarbon-molybdenum composite films have very dense structure, composed of molybdenum oxide andmolybdenum carbide composite. The molybdenum compounds are embedded in the mesoporouscarbon walls, with a particle size of4nm. In the0.5M H₂SO₄, the corrosion potential and corrosioncurrent density of mesoporous carbon-molybdenum composite films are277mV and0.0273μA cm^-2,respectively.5. In order to enhance hydrophobic property and conductivity of mesoporous carbon film,conductive graphene or carbon nanotubes are added to ordered mesoporous carbon in situ. Theconductivity is0.35and0.41S m^-1, the contact angles are90°and96°, respectively. The corrosion current density is0.140μA cm^-2 and0.008μA cm^-2, in simulated work environment of PEMFC.更多还原