A.M. Castro Luna

A novel electrocatalytic polyaniline electrode for methanol oxidation

Pt clusters were electrodispersed on polymeric films to obtain catalytic electrodes for methanol oxidation. The electrodeposit was built up by applying either a constant potential or a repetitive square wave potential routine. The performance of the electrodes was followed by measuring the stripping peak potential of adsorbed CO, each assembly metal/Pani/Pt being characterized by SEM and EDAX. Polymeric electrodes, modified with Pt electrodeposited by the programmed potential variation had a better electrocatalytic activity for CO and methanol oxidation. The novel tailored electrode is the result of a balance between a particular morphology and the number of particles of the catalytic material on the conductive polyaniline matrix.

Voltammetric behaviour of electrocatalytic poisons for the electro-oxidation of carbon monoxide, formic acid, formaldehyde and methanol on electrodispe

Abstract The voltammetric stripping of catalytic poisons arising from CO, HCOOH, HCOH and CH3OH was studied at electrodispersed Pt electrodes of different roughness factors (R) in acidic solutions. The working electrodes behave in a very reproducible way for values of R ranging from 5 to 250. Experiments were performed in a microflux cell. The results obtained with CO adsorbate show that full coverage, referred to a H-adatom monolayer as the total H-desorption charge, is attained, whereas the maximum coverage of the surface by the residues arising from the organic fuels reaches only 80–85%. The dependence of the current peak multiplicity and oxidation potential on the adsorption potential (Ead) is shown for CO adsorbate at low R. For R > 30, depolarization of the electro-oxidation reaction takes place and then the oxidation potential of the main oxidation peak remains rather insensitive to Ead. Changing the base electrolyte either from HClO4 to H2SO4 or H3PO4 with the electrodispersed electrodes allows the influence of surface heterogeneity and H-bonding effects on the stripping current multiplicity for electroadsorbed states to be enhanced.

A catalytic platinum–ruthenium–polyaniline electrode for methanol oxidation

Polyaniline films prepared on Au wires were employed as substrates to deposit Pt and/or Ru using a potential-programmed perturbation. Different compositions of Pt and Ru ions in acid electrolyte were employed to decorate the electrodes. The atomic percentages of Pt and Ru on Pani were determined by EDAX and particle size and distribution by SEM. The catalytic activity was tested for adsorbed CO and CH3OH electrooxidation. Nanoparticles of Pt–Ru with different Pt–Ru contents were obtained and characterized for each reaction.

The electro-oxidation of glucose on microcolumnar gold electrodes in different neutral solutions

Abstract The influence of the electrolyte composition on the kinetics and mechanism of glucose electro-oxidation has been investigated on microcolumnar Au electrodes. Neutral electrolyte solutions containing either sulphate, phosphate, borate or perchlorate anions were employed. The results show that the glucose electro-oxidation reaction on this type of Au electrode is favoured in those electrolytes with a high buffer capacity and is inhibited by anion adsorption. The electro-oxidation process involves the formation of weakly and strongly bound adsorbates acting as poisons. Bulk glucose electro-oxidation apparently takes place without the formation of a detectable amount of adsorbed intermediates.

Kinetics and mechanism of the electrochemical reduction of molecular oxygen on platinum in KOH: influence of preferred crystallographic orientation

The oxygen electroreduction reaction has been studied at both preferred oriented and conventional polycrystalline platinum rotating disc electrodes in xm KOH (0.05 ⩽ x ⩽ 3.0) aqueous solutions under oxygen saturation at 25°C. At low current densities, Tafel lines with slope -0.060 V decade−1 have been obtained at all platinum electrodes. At high current densities, higher Tafel slopes ranging from -0.18 to -0.40 V decade−1 have been observed, depending on the type of preferred oriented Pt and KOH concentration. Rotating ring-disc electrode data have shown that a higher amount of H2O2 is produced on one type of preferred oriented surface at all KOH concentrations. A complex reaction scheme has been used to evaluate the electrochemical rate constants of the reaction steps at three platinum electrodes.

Electroreduction of molecular oxygen on preferentially oriented platinum electrodes in acid solution

The oxygen electroreduction reaction was studied on two different preferentially oriented ((111)-type and (100)-type and on a conventional polycrystalline (PC) platinum rotating disc electrodes in acid solutions at 30 °C. At low overpotentials, Tafel lines of −0.060 V decade−1 were obtained on the three electrodes in oxygen-saturated 1.0m H2SO4 and 1.0m H2SO4 + ym K2SO4 (0 ⩽y ⩽ 1). At high over-potentials the usual Tafel slope of -0.120V decade−1 was observed on both (111)-type and PC platinum electrodes in 1.0m H2SO4, whereas a slope of −0.165V decade−1 was found on (100)-type platinum. In oxygen-saturated 1.0m H2SO4 the surface coverage by O-containing adsorbates on (100)-type platinum was greater than on both (111)-type and PC platinum. Rotating ring-disc electrode data showed that a higher amount of H2O2 was produced on (100)-type platinum than on the other platinum surfaces. The overpotential against current density plots are influenced by the anion concentration depending on the type of preferentially oriented platinum.

Temperature dependence of kinetic parameters related to oxygen electroreduction in acid solutions on platinum electrodes

The oxygen electroreduction reaction (OERR) kinetics at (111)- and (100)-type Pt electrodes has been studied in aqueous 1.0 M H2SO4 solutions in the 8–62°C range. On both Pt electrodes and at all temperatures, two Tafel regions have been observed. The Tafel slope in the low current density range is −0.053 ± 0.005 V decade−1, irrespective of temperature and the surface texture of the electrode. For (111)-type Pt, the Tafel slope in the high current density range increases with temperature, approaching the −2.303(2RT/F) ratio, whereas for (100)-type Pt, it reaches a temperature-independent value equal to −0.165 ± 0.003 V decade−1. Temperature dependences of OERR Tafel slopes on both types of Pt electrodes offer the possibility of further insights into the mechanism of the reaction, through the interpretation of both the adsorption enthalpy and entropy of intermediates produced along the OERR. Compensation effects, involving activation enthalpy and entropy variations with the applied potential, are also considered to account for experimental data.

Smooth and rough platinum deposits resulting from the electroreduction of hydrous oxide platinum overlayers—a mechanistic approach

The electroreduction of thick platinum oxides accumulated by the application of a fast square wave perturbing potential in 0.5 M H2SO4 was studied by using potentiodynamic and potentiostatic techniques complemented with scanning electron miscroscopy. The electroreduction process can be unambigously explained through an instantaneous nucleation and 3-D growth of right circular cones under charge transfer control where diffusion of reacting species to the growing centres is essential for further expansion. The growth mode of the Pt crystallites either smooth or rough depends on the electroreduction conditions. The rought/smooth modes of growth result from the influence of the electric field on the transport of particles in the reaction region and on the supersaturation concentration operating during the electrocrystallization process.

Preparation and characterization of composite polyaniline materials for catalytic purposes

Composite film electrodes were prepared by open-circuit Pt deposition on polymeric PANI films that were electrosynthesized from aniline acid solutions with suspended carbon particles (CPs). Gold, nickel, and a Ni-based alloy, Nichrome, were used as substrates, and carbon particles, carbon nanotubes (CNT), and Vulcan XC-72R carbon black, suspended in the monomer acid solution, were incorporated into the film. Pt particles were dispersed on films grown on Ni-based substrates by deposition from a Pt(IV) acid solution at open circuit (OC). CNT trapped into the PANI films have a favorable influence on Pt dispersion. The novel composite electrodes showed significant catalytic activity for methanol oxidation.

The behaviour of platinized platinum electrodes in acid solutions: correlation between voltammetric data and electrode structure

The electrochemical behaviour of platinized platinum electrodes prepared by different methods was studied in the H-adatoms and O-adatoms electroadsorption-electrodesorption potential range in 1m HClO4 at 30°C. Porous platinized platinum electrodes of different degrees of platinization prepared at a constant potential show an anomalous voltammetric behaviour. The magnitude of the anomalous effect depends on the electroplating conditions and it becomes more remarkable at the lowest voltammetric sweep rate. The anomalous behaviour is explained on the basis of absorption of hydrogen into the porous structure and its influence on the different stages of the hydrogen electrode reaction. The absorption of hydrogen occurs either during electroplating and/or during the potentiodynamic stabilization of the porous electrode.