【作者】 彭谢兰；

【导师】 谢青季；

【作者基本信息】 湖南师范大学 ， 分析化学， 2006， 硕士

【摘要】 电化学石英晶体阻抗分析（EQCIA）法是一种多参数电化学石英晶体微天平（EQCM）技术,可现场动态检测电极表面低至纳克级的质量变化及溶液粘密度、修饰膜粘弹性等参数的变化,可广泛用于电化学和电分析化学等领域的研究,尤其是研究各种电沉积过程。通过在电极表面电沉积导电高分子以制备导电高分子修饰电极一直是化学修饰电极的一个重要研究方向,然而,有关导电高分子多孔修饰膜的制备和表征的研究报道并不很多。同时,EQCI技术尚未用于研究非水电化学体系。有鉴于此,本学位论文在文献综述工作的基础上,开展了EQCI研究非水体系和多孔导电高分子修饰电极用于甲醇催化电氧化的一些创新研究工作。主要内容如下: （1） 综述了聚合物修饰电极研究领域以及EQCM在聚合物修饰电极、非水体系和直接甲醇燃料电池领域的发展历史和一些近期进展。 （2） 用电化学石英晶体阻抗分析（EQCIA）法研究了含LiClO₄·3H₂O的乙腈溶液体系,在电位环扫过程中、一定的负电位区间,频率明显下降,其他阻抗参数也有相应的响应。我们提出了合理解释该实验现象的机理是LiOH在乙腈介质中的电沉积,即电位环扫过程中,在相应的负电位区间溶解氧和共存水被电还原产生OH^-,OH^-与溶液中的Li⁺离子结合生成在乙腈中溶解度很小的LiOH。在含NaClO₄·2H₂O的乙腈溶液中也观察到类似的NaOH的电沉积现象,而在含分别含有0.1 mol L^-1（TBAC）和0.1 mol L^-1（TBAB）的乙腈溶液中,频率和其他阻抗参数的响应非常小,说明没有明显的电沉积现象。讨论了LiClO₄·3H₂O和外加水的浓度的影响。当LiClO₄·3H₂O的浓度由0.1增加到0.2 mol L^-1时,电还原产生的LiOH随着电解质浓度的增加而增加;在外加水浓度更多还原

【Abstract】 Electrochemical quartz crystal impedance analysis (EQCIA) is an multiple-parameter electrochemical quartz crystal microbalance (EQCM) method, which can be used to measure changes in electrode mass down to the nanogram level, solution viscodensity, the elasticity of modified films during an electrochemical perturbation. It has been widely used in electrochemical and electroanalytical fields, especially in monitoring various electrodeposition processes. The preparation of conducting polymer modified electrodes through electropolymerization is an important aspect in polymer modified electrode, however, there are very limited reports in preparation and characterization of conducting porous polymer film modified electrode. To date, the EQCI technology has not been used to investigate non-aqueous electrochemical systems. In this thesis, we have extended the EQCI studies for the first time to several non-aqueous systems and the preparation of porous conducting polymer modified electrodes for the electrooxidation of methanol. The main contents are summarized as follows.1. The polymer modified electrodes, the electrochemical quartz crystal microbalance, nonaqueous systems and catalysts for direct methanol fuel cell have been briefly reviewed.2. The electrochemical quartz crystal impedance (EQCI) analysis method was used for the first time to quantitatively examine the precipitation of LiOH onto a gold electrode at potentials negative to ca. -0.7 V vs SCE during the cathodic sweep reduction of dissolved oxygen and coexistingwater in acetonitrile (ACN) containing LiC104-3H20, as a result of the poor solubility of electrogenerated LiOH in the ACN medium. The suggested LiOH-precipitation mechanism was supported by comparative experiments conducted in ACN containing NaClO^I-feO (or tetrabutyl ammonium chloride/bromide), since large EQCI responses implying a similar precipitation of electrogenerated NaOH were also obtained in the NaClCv2H2O system, but the quartz crystal impedance responses were negligibly small in the two systems of quarternary ammonium salts. The effects of concentrations of LiClCv3H2O and the foreign water added in ACN on the EQCI responses were individually examined, and the maximum frequency shift induced by the LiOH precipitation was found to be as large as about -5 kHz. The cyclic voltammetric growth of polypyrrole (PPY) films at several Au electrodes in fresh ACN solutions of 1 mol L’1 pyrrole + 0.1 mol L"1 LiC104-3H20 were comparatively conducted over three potential-sweep ranges, 0 to 0.85 (A, PPYa), -1.6 to 0.85 (B, PPYB) and -2.0 to 0.85 V vs SCE, respectively, giving that the accompanying precipitation of LiOH notably influenced the polymer growth and porosity. Compared with the normal PPY film (PPYa), the PPYb after removing the LiOH precipitate formed during the cyclic voltammetric growth of the polymer was more porous, as examined by EQCI and SEM techniques, which resulted in a larger Pt dispersion when Pt particles were electrodeposited on the PPYb/Au electrode in acidic chloroplatinic solution and a higher electrocatalytic activity toward methanol oxidation in aqueous H2SO4. The proposed protocol ofincreasing the PPY porosity by introducing removable electrodeposits during PPY’s growth may be of some general interests for other polymers using other removable precipitates.3. The electrochemical quartz crystal microbalance (EQCM) method was used to quantitatively examine the precipitation of LiOH (or NaOH) onto a gold electrode at potentials negative to ca. -0.8 V vs SCE during the cathodic sweep reduction of dissolved oxygen and coexisting water in acetone, DMF, DMSO, C2H5OH or CH3OH containing hydrated perchlorate, as a result of the poor solubility of electrogenerated hydroxide in the nonaqueous medium. In contrast, the EQCM response indicative of precipitate adherence was negligibly small by using tetrabutyl ammonium bromide as the supporting electrolyte. Effects of electrolyte and its concentration, solvent, water content on electrodeposition of hydroxide were discussed, and the electrode-collection efficiency of the precipitate was evaluated.4. We conducted the co-precipitation of quinone-hydroquinone charge transfer salt with polyaniline for the preparation of porous polyaniline film in acid solution, being tracked by EQCM technique. The porous polyaniline film was used as the platinum substrate for methanol electrooxidation. In comparison with a normal polyaniline film, the porous polyaniline film exhibited a higher catalytic efficiency by a factor of ca. 2.4. The effect of hydroquinone concentration on the porosity of polyaniline film was studied. When the concentration of hydroquinone was 0.3 mol L" , the catalytic efficiency for electrooxidation of methanolbecame maximum. The effect of Pt loading mass was also discussed, giving an optimal Pt loading mass of 160 ug cm" .更多还原