A kinetic study for the electrosynthesis of polypyrrole (Ppy) doped with SO(4)(2-) ions is presented. Ppy films were electrochemically polymerized onto a graphite-epoxy resin electrode. Experimental current density transients (j-t) were obtained for three different potentiometric behaviors: anionic, cationic, and a combination. Theoretical models were used to fit the experimental j-t data to determine the nucleation and growth processes controlling the polymer synthesis. It was encountered that, in all cases, pyrrole electropolimerization involves two concomitant processes, namely, a Ppy diffusion limited multiple 3D nucleation and growth and pyrrole electro-oxidation on the growing surface of the Ppy nuclei. SEM analysis of the electrodes surfaces reveals that Ppy deposition occurred over most of the electrode surface by multiple nucleation of hemispheres, as the theoretical model used for the analysis of the current transients required. Hemispherical particles formed the polymeric film displaying different sizes. The order for the particle size was as follows: anionic > anionic-cationic > cationic. These results are congruent with those obtained by theoretical analysis of the corresponding current transients. Analysis of the impedance measurements recorded on the anionic Ppy film, immersed in an aqueous solution with different sulfate ion concentrations evidenced that SO(4)(2-) ions diffuse through the Ppy film provoking a decrease of its electrical resistance and an increase of its dielectric constant. From the Warburg impedance coefficient, the sulfate coefficient of diffusion in the Ppy film was 1.38 x 10(-9) cm(2) s(-1).

In this work, polypyrrole films are electrosynthesized in aqueous media over graphite-epoxy resin composite; sulphate ions used to dope the polymer are obtained from different salts (Na 2 SO 4 , Li 2 SO 4 , (NH 4 ) 2 SO 4 and K 2 SO 4 ). Potentiostatic techniques are used to induce the polymerization. Potentiometric response of Ppy-SO 4 -2 films was evaluated by calibration curves. Analyzing the slope sign, behavior of the different films can be classified in three responses: anionic, cationic and anionic-cationic. These behaviors were observed for all synthesized films, independently of the sulphate salt used. When analyzing the transients obtained for the different salts, similarities where found for those with the same potentiometric behavior, but significative differences were observed when comparing transients of different potentiometric response. It was determined that the cation size of the sulphate salt influences the Ppy-SO 4 -2 film response. Boundaries on the potentiostatic synthesis parameters are suggested to induce a specific potentiometric response.

A kinetic study for the electrosynthesis of polypyrrole (Ppy) doped with SO 4 -2 ions is presented. Ppy films are electrochemically polymerized over graphite -epoxy resin electrode. Cyclic voltammetry shows a non-reversible process and the charge density increases as the number of cycles increases too. Current transients are obtained for three different potentiometric behaviors: anionic, cationic and a combination of both. Experimental data was statistically fitted to theoretical models to determine the nucleation and growth processes governing the polymer synthesis. Statistical fit suggests that the mechanism involved in the electropolimerization process is 3D nucleation limited by diffusion of the electroactive specie. The anionic-response polymer displays the lowest diffusion coefficient, while the cationic-response polymer displays the highest one. In all cases, both the active-sites number and the nucleation rate have considerably high values.

A study is presented on the electrochemical oxidation of 4-chlorophenol (4cp) in aqueous solution using a bare carbon paste electrode, CPE, and another one that was modified with ZnAl layered double hydroxides (CPE/ZnAl-LDH). The electro-oxidation was effected at pH values ranging from 3 up to 11. It was found through cyclic voltammetry that this process was irreversible, namely, there were no reduction peaks, and that depending on the nature of the electrode, the anodic current was limited either by adsorption (CPE) or diffusion (CPE/ZnAl-LDH). The energy required and the oxidation reaction rate depended on the pH and on the nature of the electrode, such that the greater rates were obtained when the CPE/ZnAl-LDH electrode and acid pHs were used.

In this work, the catalytic activity of copper-palladium (Cu-Pd) nanoparticles (NPs) is studied for formic acid oxidation. The Cu-Pd NPs were synthesized in a toluene/water system at room temperature. The synthesis of organic phase containing the metal ions was carried out as follows: the aqueous solutions containing the cooper and palladium metals ions, Cu(NO3)2 and PdCl2. Cu and Pd were mixed in appropriate amounts to obtain aqueous solution with 1:1 molar ratios of Cu:Pd. The toluene solution of hexadecylamine (C16H33NH2) was added to the Cu and Pd aqueous solution under strong stirring. For the mixture solution, an immediate two-layer separation was produced, with a light yellow organic phase on the top and a yellow tinted aqueous phase on the bottom. Ions were allowed to diffuse gradually into the organic phase by complexing them with the amine. Cu-Pd NPs were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and energy dispersive X-ray (EDX) analysis. The catalytic activity of Cu-Pd NPs was evaluated for formic acid oxidation, using the anodic current density. The electrochemical result shows that Cu-Pd NPs present a higher catalytic activity than Pd NPs.