Arturo Estrada-Vargas

Carbon nanotubes/carbon xerogel-nafion electrodes: a comparative study of preparation methods

We report the preparation and electrochemical characterization of carbon nanotubes (CNT)/carbon xerogel-nafion (CXN) electrodes obtained by casting carbon nanotube inks on carbon xerogel-nafion matrixes under terrestrial (g) and enhanced (13 g) gravity. The impregnated electrodes were compared with composites prepared by mixing CXN dispersions with CNT inks. For casted CNT, alternate current scanning electrochemical microscopy studies along the film-electrode area showed differences that can be correlated with the position of the electronic conducting CNT phase on the more resistive matrix. It revealed the transition from a conductive to dielectric surface when impregnation takes place at terrestrial and enhanced gravity, respectively. Although the addition of CNT enhances the capacitance and mechanical properties of CXN in all preparation methods, the largest specific capacitance was observed in electrodes impregnated at 1 g. Electrodes prepared by mixing and those casted at 13 g show similar capacitance values regardless of contrasting conductivity. A mechanism explaining the microstructural, electrical, and adsorptive differences brought out by the various preparation methods is proposed.

Kinetic Passivation Effect of Localized Differential Aeration on Brass

The formation of a localized differential aeration cell on metals, susceptible to both anodic and cathodic corrosion, is a serious threat because of multiple degradation processes commencing with the passivation layer destruction. By using local electrochemical and X-ray dispersive techniques, it has been demonstrated that the differential aeration cell formed on high brass (α-brass, Cu65-Zn35) in the presence of 1H-benzotriazole or 5-methyl-1H-benzotriazole plays both corrosion-inhibiting and accelerating roles, depending on the inhibitor exposure time. Alternating-current scanning electrochemical microscopy was used to image local electrochemical activity, whereas energy-dispersive X-ray spectroscopy provided evidence for the mechanism of the observed phenomena. Short-term exposure to the inhibitor (5 min) promotes the formation of a passivation layer in the waterline region. In contrast, after prolonged exposure (45 min), a deficient passivation layer develops for both inhibitors. An excess of zinc(II)-inhibitor complexes in the passivation layer is accountable for the corrosion resistance of the region with high differential aeration. Rapid dezincification and local alkalinization facilitate the initial rapid formation of a passivation layer in the area under differential aeration to preserve its composition upon further modification.

Localized Impedance Measurements in Different Redox Potential Metals and their Galvanic Coupling by Using AC-SECM

In recent years, the use of Scanning Electrochemical Microscopy in its Alternating Current mode (AC-SECM) has increased due to its capability for detecting and interpreting local variations of electrochemical properties on surfaces with high spatial resolution. In this paper, we intend to extend the applications of AC-SECM for identifying local impedance variations on surfaces of materials with different redox potential, immersed in resistive media such as tequila in presence of supporting electrolyte. Preliminary results are promising since it is possible to visualize boundaries of materials with different redox potential by means of localized impedance measurements, which opens a new perspective for studying composite materials such as minerals.

Carbon Electrodes Surface Modification in Hexane/CTAB-CTAmodified-butanol/Water System

The modification of graphite electrode surfaces with different hardness using hexane/CTAB-CTAmodified-butanol/water microemulsion forming system with inverse micelles (W/O) is presented. CTAB is modified by exchanging bromide ions of the surfactant with ferrocyanide ions in a salt solution. Carbon electrodes are modified by immersing them into a W/O microemulsion, followed by a rinsing step with pure water, and a potential cycling in a ferrocyanide solution. After this treatment, electrodes display two redox peaks, characteristic of strongly adsorbed species. The amount of adsorbed material at the electrode surface is greater for soft graphite electrodes than for hard ones. FTIR spectra of carbon electrodes before and after modification not show signal of C-C bonds and the increase of C-N signal from ferrocyanide ions attached to the surfactant. These results support the formation of a new bond between the surfactants tail and the carbon surface.

Voltammetric Characterization of Liquid/Liquid Interfaces Modified with Cetyl-Trimethyl-Ammonium Bromide (CTAB)

Chemical Engineering Department, University of Guadalajara, Guadalajara, Jalisco 44430, Mexico In this paper a voltammetric study of a three-phase system modified with the surfactant CTAB in a liquid/liquid interface is presented. The three-phase system consists of a nitrobenzene microdroplet (1µL) with 0.1 M ferrocene, immobilized in a paraffin impregnated graphite electrode and immersed in a LiClO