Piezoelectric Electrochemistry Studies On Nonaqueous Systems And Porous Polymer

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" .