碳原子线对于甲醇电化学氧化的作用

【作者】 魏日兵；

【导师】 薛宽宏；

【作者基本信息】 南京师范大学 ， 应用化学， 2007， 硕士

【摘要】 由本实验室合成的新型碳材料，碳原子线（carbon atom wires，CAWs），不仅可用作甲醇电化学氧化反应的催化剂载体，而且对该反应还兼具助催化作用。利用透射电子显微镜（TEM）、X射线衍射（XRD）等手段对碳原子线合成产物的形貌、结构进行了表征；采用循环伏安法考察了Pt／CAWs／G电极在甲醇氧化过程中的电催化性能，并与以VulcanXC—72活性碳粉为载体的Pt／XC／G电极作比较。实验表明，与Pt／XC／G电极相比，在相同Pt沉积电量的情况下，Pt／CAWs／G电极上的Pt表面积增加1倍，循环伏安曲线（CV）上的甲醇氧化峰电流密度增加1.4倍。碳原子线的结构、形貌与其制备条件有关。研究了CAWs制备条件，如催化剂含量、热解温度等，对于Pt／CAWs／G电极对甲醇电催化氧化的影响。实验表明，CAWs的最佳制备条件是热解温度为，750℃，催化剂与热解前驱体的质量比为8‰。由于铁、钴、镍作为过渡金属具有许多相似的化学性质，我们尝试以钴、镍代替铁作为催化剂制备CAWs。实验表明，在相同Pt沉积电量的情况下，Pt／CAWs（Ni）／G电极的Pt的表面积比Pt／CAWs_Fe／G电极增加50％，Pt／CAWs（Co）／G电极的Pt的表面积与Pt／CAWs（Fe）／G电极相近，三种电极在循环伏安曲线上的甲醇氧化峰电流密度相近。相对于Pt／CAWs_Fe／G电极而言，Pt／CAWs（Ni）／G电极和Pt／CAWs（Co）／G电极对甲醇氧化的稳定性稍有增强。CAWs经过硝酸处理可以起到纯化和增加表面基团的作用，从硝酸处理前后的CAWs红外光谱得知，经硝酸处理的碳原子线具有更多的羟基和羧基。在对甲醇的电催化氧化中，相同Pt沉积电量的情况下，由经硝酸处理的碳原子线作载体的Pt／CAWs（硝酸）／G电极的Pt的表面积与未经硝酸处理的碳原子线作载体的Pt／CAWs／G电极相近，Pt／CAWs（硝酸）／G电极在循环伏安曲线上的甲醇氧化峰电流密度比Pt／CAWs／G电极高1倍左右，在稳定性方面Pt／CAWs（硝酸）／G电极明显优于Pt／CAWs／G电极。更多还原

【Abstract】 Carbon atom wires （CAWs）, a new novel carbonaceous material synthesized in our lab, act as both of a catalyst carrier and a catalyst promoter in electrochemical oxidation of methanol.The morphology and structure of the pyrolytic product of CAWs were characterized by transmission electron microscope （TEM） and X-ray diffraction （XRD）. The catalysis of the Pt/CAWs/G electrode on electrochemical oxidation of methanol was demonstrated by cyclic voltammetry. Experimental results showed that, the Pt surface area increased by 1 time and anodic peak current of cyclic votammograms （CVs） increased by 1.4 times on the Pt/CAWs/G electrode, compared to the Pt/XC/G electrode, at which Pt was carried on active carbon VulcanXC-72, when the same charge quantity was consumed to deposit Pt on these electrodes.The structure and morphology of CAWs depend on their synthetic conditions, such as catalyst quantity added and pyrolytic temperature applied in synthesis, which were investigated for the effects of Pt/CAWs/G electrode on electrocatalytic oxidation of methanol. The experimental results gave the optimal pyrolytic temperature of 750°C and the optimal mass ratio of 8‰, of the catalyst to pyrolytic precursor.Considering the similar chemical properties among Fe, Co and Ni, we tried to use Co or Ni, instead of Fe, as the catalyst in CAW preparation. Experimental results indicated that, with the same charge quantity for Pt deposition, the surface area of Pt on the Pt/CAWs_（Ni）/G electrode increase by 50% in comparison with the Pt/CAWs_（Fe）/G, or Pt/CAWs_（Co）/G electrode; the three electrodes almost have the same anodic peak current density of methanol oxidation on their CVs; the electrodes of Pt/CAWs_（Ni）/G and Pt/CAWs_（Co）/G showed little better stability compared to Pt/CAWs_（Fe）/G electrode.Nitric acid treatment on CAWs can improve their purity and increase functional groups such as hydroxyl and carboxylic acid groups attached on them, confirmed by the infrared spectra measured before and after the treatment respectively. With the same charge quantity consumed for Pt deposition, the anodic peak current density of methanol oxidation at CVs on the Pt/CAWs_（Nitric）/G electrode with nitric acid treatment, increased by 100% compared to the Pt/CAWs/G electrode without nitric acid treatment, although they have the same value of the surface area of Pt. The former electrode has much superiority over the latter on steadiness.更多还原