【作者】 宛朝辉；

【导师】 潘牧；

【作者基本信息】 武汉理工大学 ， 材料学， 2007， 硕士

【摘要】 提出了一种采用静电自组装技术合成直接甲醇燃料电池（Direct Methanol Fuel Cell，DMFC）用抗甲醇渗透质子交换膜（Methanol Blocking Membrane，MBM）的方法，从理论上分析了自组装方案和自组装抗甲醇渗透质子交换膜（Self-assembled MBM，SA-MBM）降低甲醇渗透、保持高的质子电导率的可行性。以此为依据合成了一种阳离子修饰的纳米Pt、Pd颗粒并运用静电自组装技术将这种Pt、Pd颗粒组装到Nafion膜表面形成DMFC用SA-MBM，。这种SA-MBM不仅在理论上可以实现有针对性的组装到Nafion膜表面的形成甲醇渗透通道的磺酸根团簇的出口和入口，从而大大降低甲醇透过率，而且制备的金属胶体颗粒直径大于质子交换膜内没有磺酸根侧链的晶相疏水区通道的直径，但小于磺酸根团簇的直径，不会进入质子交换膜内部对膜的质子传导能力产生影响。这种SA-MBM在质子交换膜越来越薄的研究趋势下仍然保持膜的低甲醇渗透率具有一定的研究价值，研究同时发现：（1）采用聚二烯丙基二甲基氯化铵（poly diallyldimethylammonium chloride，PDDA）修饰的方法制备金属胶体颗粒，PDDA是以N元素相邻的仲碳和间位的叔碳与其相连。在整个pH值范围胶体均带正电，并且在PDDA的位阻作用下使得胶体能稳定的存在。在金属胶体颗粒合成过程中，金属颗粒前驱体的浓度越低、PDDA的浓度越大、溶液的pH值越高以及还原剂的还原性越强，合成的金属颗粒就越小。通过控制这些条件分别合成了粒径范围为2.1～5.8nm的PDDA-Pt颗粒和粒径范围为2.5～6.2nm PDDA-Pd。（2） PDDA修饰的Pt和Pd金属颗粒只会组装到Nafion（?）膜的表面，不会进入膜的内部，因而在膜的表面形成修饰层；通过改变NaCl溶液浓度来调节Nafion（?）膜表面电荷密度以及Nafion（?）膜在胶体中的浸渍时间，可以控制胶体颗粒在Nafion（?）膜表面的组装量（3）与组装前的Nafion^?1135膜相比，组装后的Nafion^?1135膜的质子电导率仅有非常小程度的下降；随着组装金属胶体颗粒粒径的增大，电导率也随之下降，但下降的幅度也非常小；就不同元素Pt和Pd对电导率的影响比较而言，粒径相当时，Pd组装的质子交换膜的质子电导率要略微高于Pt组装的质子交换膜。组装后的Nafion^?膜比组装前的Nafion^?膜甲醇扩散系数要低的多；对于不同种类的金属，当金属粒径相当时，甲醇扩散系数也基本一致；随着金属颗粒粒径的增大，甲醇扩散系数也进一步的下降。当金属粒径达到4.5nm后，甲醇扩散系数随金属粒径的变化不大，基本保持在5.20～5.40×10^-7cm²／s。组装金属颗粒后，甲醇相对选择系数都会增大。而且随着金属粒径的增大，甲醇相对选择系数也随之增大。当Pt和Pd颗粒粒径大于4.5nm后甲醇相对选择系数基本保持不变。当Pt颗粒粒径为4.5nm时，其甲醇相对选择系数增大到3.95；当Pd颗粒粒径为4.7nm时，其甲醇相对选择系数增大到4.27。金属粒径相当时，Pd的甲醇相对选择系数比Pt的甲醇相对选择系数要大。组装膜的开路电压（OCV）均比纯Nafion膜的OCV高，其值从纯Nafion的0.620V增加到组装5.8nm Pt颗粒阻醇膜的0.745V和组装6.2nm Pd颗粒阻醇膜的0.757V。自组装膜比纯Nafion膜的输出功率要高，且组装4.5nm左右粒径的的阻醇膜性能最佳。单电池的Ⅰ-Ⅴ极化曲线结果与质子交换膜的甲醇相对选择系数a相关：a越大，单电池输出性能越好；反之，a越小，单电池输出性能越差。组装的金属颗粒达到5.8nm以上的组装膜的OCV虽然最高，但在电流密度为100mA以后，比组装4.5nm左右粒径的组装膜单电池性能稍差。更多还原

【Abstract】 Fabrication of methanol blocking membrane （MBM） via electrostatic self-assembly technology was put forward in order to suppress methanol crossover and maintain high proton conductivity of proton exchange membrane. The feasibilities and advantages of fuel cell with self-assembled MBM were discussed theoretically. Accordingly, charged platinum and palladium nano-particles modified with PDDA ionmers were synthesized in the study. The charged particles were electrostaticly self-assembled on Nafion membrane surface and a novel self-assembled methanol blocking membrane （SA-MBM） for direct methanol fuel cell （DMFC） was fabricated. In the SA-MBM, all Pt and Pd particles contact closely with -SO3^- of Nafion membrane. So it is reasonable to consider that all particles are located in the exit and entrance of methanol channels and has favorable methanol blocking efficiency. Moreover, the particles are too large to enter Nafion membrane, which enable us to maintain high proton conductivity. At the same time, some conclusions had been summarized as following:（1） The obtained charged platinum and palladium particles modified with PDDA, PDDA contact Pt and Pd particles with carbon element. The modified Pt and Pd particles contained positive charge in all pH value range and were stabled with electrostatic and steric effect of PDDA. The particle size of Pt and Pd had obvious correlation with concentration of metal precursor and PDDA, pH value of the solution, and redox of reducer. The particle size of Pt and Pd would minish when content and pH value of the PDDA increase, concentration of metal precursor decrease, and redox of reducer increase; The obtained charged Pt and Pd particles modified with PDDA were sized with 2.1～5.8 nm、2.5～6.2nm in average respectively, by controling reaction condition.（2） All platinum and palladium particles modified with PDDA particles are located in the exit and entrance of methanol channels and without entering Nafion membrane. And the distribution of these particles can be controlled from denseness to sparseness by adjusting the concentration of NaCl solution and dipping time of Nafion（?） membrane in colloidal solution.（3） It is found the proton exchange membrane self-assembled with metal particles have the lower methanol crossover. When the diameter increased, the methanol-crossover and relative selectivity of the membrane increased. When increase the particles size than 4.5 nm had little influence on the methanol-crossover, and their methanol diffusion coefficient were almost 5.20～5.40*10^-7cm²/s, relative selectivity were 3.95 and 4.27 for Pt and Pd particles, respectively. The proton conductivity of the proton exchange membrane also was influence by the particles size. The proton conductivity decreased with little increase of the particles size, and the proton conductivity of self-assembled membrane with Pt paticles are little lower than the Pd particles’. All the self-assembled membranes have higher OCV and performance than original Nafion membrane. When the particles size were 5.8nm and 6.2nm for Pt particles and Pd particles, they would have the highest OCV, 0.745V and 0.757V, respecvtively, due to the reciprocal of the methanol permeation current density and membrane area resistance.methanol diffusion coefficient were almost 5.20～5.40*10^-7cm2/s. The Current-Voltage （I-V） curves show that the self-assembled PEMs have better output than that of the pure Nafion membranes. And their output relate with relative selectivity, the higher relative selectivity, the more output.更多还原