Gabriel A. Planes

Redox coupled ion exchange in cobalt oxide films

Ion exchange coupled to oxidation–reduction cycling of electrochromic cobalt oxide films was studied using Probe Beam Deflection (PBD) techniques. The films were deposited by potentiodynamic cycling of glassy carbon electrodes in aqueous Co+2 solution. The cyclic voltammograms of cobalt oxide films present three peaks in basic (pH=13) solution. The PBD signal is positive during oxidation indicating insertion of hydroxide ions. The results are confirmed by monitoring the PBD signal during pulse potential experiments at varying distances of the beam from the electrode. Using the theory of PBD behaviour for discontinuous reactions, a diffusion coefficient for the mobile ion of 1.68×10−5 cm2/s was measured, which agreed with that observed for NaOH diffusion in similar systems. The results are explained on the basis of a scheme of solid state oxidations from CoII to CoIV in three redox steps, coupled to hydroxide ion insertion.

Synthesis of atomic gold clusters with strong electrocatalytic activities.

Small atomic gold clusters in solution, Au n , stabilized by tetrabutyl ammonium bromide (TBABr), have been synthesized by a simple electrochemical technique, based on the anodic dissolution of a gold electrode in the presence of TBABr salt, and using acetronitrile as solvent. The presence of clusters in the range Au3-Au11 were detected by MALDI-TOF spectroscopy, and further characterized by UV-vis absorption spectroscopy, TEM, AFM, X-ray diffraction, and cyclic voltammetry. Clusters display a semiconductor behavior with a band edge of approximately 2.5 eV. We report here their extraordinarily high electrocatalytic activity toward the O2 reduction reaction in acid solutions, which can explain Zhangs results, showing that a four-electron mechanism seems to occur because of the facile reduction of H2O2 on gold clusters compared to bulk gold or larger gold nanoparticles.

A soluble and electroactive polyaniline obtained by coupling of 4-sulfobenzenediazonium ion and poly(N-methylaniline)

Abstract A modified polyaniline was obtained by coupling of the 4-sulfobenzenediazonium ion with poly ( N -methylaniline) (PNMANI) at temperatures below 5°C and in basic or neutral pH conditions. The FT-IR spectra of the product show all bands due to the poly( N -methylaniline). Additional bands at 1007, 1003 and 623 cm −1 are assigned to the vibrations of the sulfonate group, incorporated in the polymer matrix. A new band at 1485 cm −1 is also present, assigned to the stretching of the azo bond. The polymer is soluble in aqueous base. The results suggest the formation of an azo-substituted poly ( N -methylaniline): poly(4-sulfobenzenazo-( N -methylaniline)) (p(4SBA-NMANI)). The solution spectra show absorption bands at 242, 310 and 595 nm. Thin films deposited on glassy carbon show clear electroactivity. The method could be used to produce electroactive films with bonded functionalities.

Double layer properties of carbon aerogel electrodes measured by probe beam deflection and AC impedance techniques.

Probe beam deflection (PBD) and AC impedance are used to quantitatively evaluate the double layer properties of carbon aerogel electrodes in aqueous media (NaF). The measurements allow determination of the potential of minimum charge of the material.

New methods of polyaniline functionalization

Abstract Novel synthetic methods of PANI functiooalization are described. We investigated coupling of diazonium salt and electrophilic nitration of the aromatic ring, amine group protection by amide formation, nucleophilic reaction with activated aromatic moieties and nucleophilic addition of sulfite ions to the ring. The structure of the products and their properties were studied by FTIR, UV-vis spectroscopy and electrochemistry.

Probe beam deflection study of ion exchange in self-assembled redox polyelectrolyte thin films

Probe beam deflection during chronoamperometric oxidation-reduction of osmium complex in layer-by-layer self-assembled redox active polyelectrolyte multilayers has shown that the nature of the charge in the topmost layer determines the ion flux that balances the redox charge.

Synthetic Porous Carbon as Support of Platinum Nanoparticles for Fuel Cell Electrodes

Porous vitreous carbon can be produced by pyrolysis of resorcinol-formaldehyde porous resin. Using surfactants as stabilizers, it is possible to dry the porous resin in air without pore collapse. Having a large surface area (>500 m2/g) and high electronic conductivity makes the materials suitable as support of electrocatalyst nanoparticles. Pt nanoparticles were prepared by a microemulsion method and impregnated into the carbon pores by adsorption from its suspension. The presence of the Pt nanoparticles is easily detected by the electrochemical reduction of proton and the evolution of H2, detected by DEMS. The cyclic voltammogram of the modified electrode in presence of CO does not show current due to CO oxidation to CO2. On the other hand, the differential electrochemical mass spectroscopy (DEMS) signal clearly shows CO2 production. Methanol can be electroxidized on the electrode containing Pt nanoparticles supported on porous carbon.

Synthesis of ultra-small cysteine-capped gold nanoparticles by pH switching of the Au(I)-cysteine polymer.

We report a synthetic approach for the production of ultra-small (0.6 nm) gold nanoparticles soluble in water with a precise control of the nanoparticle size. Our synthetic approach utilizes a pH-depending Au-cysteine polymer as a quencher for the AuNPs grown. The method extends the synthetic capabilities of nanoparticles with sizes down to 1 nm. In addition to the strict pH control, the existence of free -SH groups present in the mixture of reaction has been observed as a key requirement for the synthesis of small nanoparticles in mild conditions. UV-Vis, SAXS, XANES, EXAFS and HR-TEM, has been used to determinate the particle size, characterization of the gold precursor and gold-cysteine interaction.

Electroanalysis using modified hierarchical nanoporous carbon materials

The role of the electrode nanoporosity in electroanalytical processes is discussed and specific phenomena (slow double layer charging, local pH effects) which can be present in porous electrode are described. Hierarchical porous carbon (HPC) materials are synthesized using a hard template method. The three dimensional carbon porosity is examined using scanning electron microscopy on flat surfaces cut using a focused ion beam (FIB-SEM). The electrochemical properties of the HPC are measured using cyclic voltammetry, AC impedance, chronoamperometry and Probe Beam Deflection (PBD) techniques. Chronoamperometry measurements of HPC seems to fit a transmission line model. PBD data show evidence of local pH changes inside the pores, during double layer charging. The HPC are modified by in situ (chemical or electrochemical) formation of metal (Pt/Ru) or metal oxide (CoOx, Fe3O4) nanoparticles. Additionally, HPC loaded with Pt decorated magnetite (Fe3O4) nanoparticles is produced by galvanic displacement. The modified HPC materials are used for the electroanalysis of different substances (CO, O2, AsO3(-3)). The role of the nanoporous carbon substrate in the electroanalytical data is evaluated.