【作者】 黄青丹；

【导师】 吴颖民； 李伟善；

【作者基本信息】 华南师范大学 ， 物理化学， 2007， 硕士

【摘要】 近年来发展起来的直接甲醇燃料电池（DMFC）由于其燃料来源丰富、价格便宜、运输和储存较为安全的优点而受到广泛重视。然而，阳极催化剂的低催化活性和甲醇氧化中间体羰基物对阳极催化剂的毒化问题致使DMFC的实际应用发展速度一直没有预期的快。为了提高Pt的活性，本论文采用循环伏安和恒电位的方法共沉积制备了Pt、Pt-H_xMoO₃和Pt-H_xMoO₃-Nafion等催化剂，利用循环伏安、电位阶跃等电化学方法，结合扫描电镜、红外光谱和能量散射光谱等物理分析测试手段，研究了所制备催化剂的形貌、对甲醇催化氧化的活性及其稳定性，并在此基础之上探讨了氢钼青铜的助催化氧化机理。主要结果如下：1．用循环伏安法可在玻炭电极上制备不同含量的铂和铂-氢钼青铜共沉积催化剂。单纯沉积铂的真实铂面积随着循环次数的增加而增加，并且沉积铂对甲醇的催化活性只取决于铂的真实面积；共沉积铂-氢钼青铜对甲醇氧化的催化能力与共沉积铂钼的比例有关，当制备催化剂所用的溶液中氯铂酸与钼酸钠的摩尔比为2∶1时，共沉积催化剂的催化活性最高，此时甲醇在共沉积催化剂上的氧化峰电流是单纯铂的1.63倍。通过考察甲醇氧化峰电流对催化剂的铂真实表面积和沉积氢钼青铜量的依赖关系后发现，沉积氢钼青铜对提高铂的催化活性有双重作用。一是分散作用，沉积氢钼青铜使沉积铂更加分散，增大了铂的真实表面积；二是质子溢出效应，氢钼青铜通过不同质子含量的氧化还原电对，H_yMO₃／H_xMO₃（y＜x＜2），不断结合质子使铂表面的吸附中间体更易氧化。2．铂催化剂在碱性溶液中对甲醇的催化氧化峰电位比酸性溶液中提早了约600mV。在Pt-H_xMoO₃催化剂对甲醇的催化氧化过程中，由氢钼青铜所产生的质子溢出效应只在酸性环境中存在，在中性和碱性环境中并不存在。Pt-H_xMoO₃在酸性、中性和碱性环境中均不稳定，H_xMoO₃会逐渐溶解于溶液中，且酸度越高，稳定性越差。3．利用复合电沉积方法，将金属铂、氢钼青铜和全氟磺酸物（Nafion）颗粒共沉积在玻碳电极上，制备出了Pt-H_xMoO₃-Nafion共沉积催化剂。与无Nafion颗粒的Pt-H_xMoO₃催化剂相比，Pt-H_xMoO₃-Nafion对甲醇的催化氧化活性及其稳定性均有明显提高。当电解液中Nafion的质量百分比浓度为0.012％时，所制得的Pt-H_xMoO₃-Nafion催化剂对甲醇的催化氧化活性最好，此时其活性提高的幅度约为75.3％，在经5000s的对甲醇长时间催化氧化后，其活性基本保持不变。经能量散射光谱（EDX）检测可知：在Pt-H_xMoO₃-Nafion表面Nafion颗粒的摩尔百分比为0.57％。经扫描电镜（SEM）观测可发现：Pt-H_xMoO₃-Nafion表面的催化剂颗粒比未共沉积Nafion之前的催化剂颗粒分布规则而且均匀。更多还原

【Abstract】 Recently direct methanol fuel cell （DMFC） has been received widespread attention due to the abundant source, the low price, the safety of the storage and transportation of the fuel. Nevertheless, the step toward the practical application has not been gone as fast as expected. There are two reasons for this slow progress. One is low electrocatalytic activity of the anodic catalyst, the other is the poisoning of the anode catalysts by the adsorbed carbonyl species derived from methanol oxidation. In this thesis, in order to improve the electrocatalytic activity of the Pt, the electrochemical co-deposition methods by cyclic voltammetry and potentiostatic were used to prepare catalysts Pt, Pt-H_xMoO₃ and Pt-H_xMoO₃-Nafion. Several electrochemical methods including cyclic voltammetry and potential step, as well as physcial analytical methods including SEM, IR and EDX were used to analyze the morphology of catalyst and the electrocatalytic activity and stability for the methanol oxidation. Besides, the electrocatalytic mechanism of hydrogen molybdenum bronze was discussed on the base of results obtained. The main results are as follows:1. Platinum and platinum-hydrogen molybdenum bronze with various amount of platinum and/or hydrogen molybdenum bronze could be prepared on a glass carbon electrode. The real surface area of the prepared platinum increases with increasing cycle number for electrode preparation and the electrocatalytic activity of the catalysts toward methanol oxidation only depends on the real surface area of platinum. However, the electrocatalytic activity of platinum-hydrogen molybdenum bronze is related to the ratio of platinum and molybdenum. It reaches its maximum when the molar ratio of platinum and molybdenum in the solutions for the electrode preparation is 2:1. In this case the oxidation peak current of methanol on the platinum-hydrogen molybdenum is 1.63 times that on the platinum. Considering the dependence of the oxidation peak current of methanol on the real surface area and the ratio of platinum and molybdenum, it is found that there are double effects of hydrogen molybdenum bronze in the improvement of electrocatalytic activity of platinum. One is dispersing effect, the real surface area of platinum is increased by the co-deposition of platinum and hydrogen molybdenum bronze. The other is proton spillover effect, the hydrogen molybdenum bronze continually accepts proton from the methanol oxidation on platinum by the oxidation and reduction of couple H_xMO₃/H_yMO₃ （y＜x＜2）, and makes it easier for the oxidation of adsorbed intermediates on platinum.2. The methanol oxidation of platinum prepared by CV on glass carbon took place in the alkaline solution at the potential 600mV more negatively than in the acid solution. The proton spillover effect from the redox couple H_xMO₃/H_yMO₃ （y＜x＜2） works in the acid solution while it does not in the alkaline and neutral solutions. The hydrogen molybdenum bronze is not stable in acid, neutral andkaline solutions, and the higher the acid concentration, the worse the stability is.3. Pt-H_xMoO₃-Nafion was prepared by cyclic voltammetry method. Compared with electrode Pt-H_xMoO₃, the electrocatalytic activity and stability of Pt-H_xMoO₃-Nation toward methanol oxidation were improved. The elecrocatalytic activity of Pt-H_xMoO₃-Nafion reaches its maximum when the content of Nation in solution is 0.012%（wt） when it is prepared by cyclic voltammetry. In this case the oxidation peak current of methanol on Pt-H_xMoO₃-Nafion is 1.758 times that on Pt-H_xMoO₃, and the electrocatalytic activity was not dropped after 5000 seconds when it was polarized in lmol/LCH₃OH+0.5 mol/L H₂SO₄ solution at 0.3V（vs Hg-Hg₂SO₄）. The content of Nation in Pt-H_xMoO₃-Nafion is 0.57%（mol） from the EDX analysis. From the SEM image of the surface of Pt-H_xMoO₃-Nafion, it can be seen that the particles on Pt-H_xMoO₃-Nafion is more uniform than that on Pt-H_xMoO₃.更多还原