Fast faradaic processes observed during the potentiodynamic polarization of polycrystalline palladium in acid electrolyte

Two almost reversible electrochemical systems are detected during the potentiodynamic anodization of polycrystalline palladium in 1 M H2SO4 and 1 M HClO4 by applying the triangular modulated triangular potential sweep technique. The first electrochemical system which appears in the 0.7–0.9 V range (vs. RHE) corresponds to the reaction Pd+H2O=PdOH+H++e− whose reversible potential is estimated as 0.80±0.02 V and the average half-life time of PdOH species is estimated as 6×10−3 s. The second electrochemical system appears when the anodizing potential sweep extends to the oxygen evolution potential region. The appearance of the second electrochemical system is accompanied by a change in colour of the electrode surface, a shift of the current-potential curve of the oxygen evolution reaction and an increase in thickness of the oxide anodic layer. The reversible response is tentatively assigned to the PdO2/PdO3 redox couple.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Changes in the polycrystalline gold electrode surface produced by square wave potential perturbations

The electroreduction of gold oxide layers produced by a square wave potential signal (SWPS) under a proper set of perturbation conditions yields a reproducible electrode surface with a large increase in the surface area. The different variables are systematically investigated to establish the optimal conditions of the SWPS. The results are discussed on the basis of the thermodynamics and kinetics of oxide monolayer and multilayer formation.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Effect of the Pt/Ru intermetallic boundary on the carbon monoxide electrooxidation: Excess electrocatalytic activity

The carbon monoxide oxidation reaction was studied on smooth Pt, Ru and Pt/Ru (Ru partially covered by Pt islands) rotating disc electrodes on acid solution saturated with CO gas (PCO = 1 atm) through steady state measurements. The current density vs. overpotential plot of the Pt/Ru electrode shows a profile qualitatively similar to the sum of both curves corresponding to pure Pt and Ru. On this basis, the excess electrocatalytic activity was defined as the difference between the current densities of the bimetallic electrode and those corresponding to the pure metals, which allowed evaluating the contribution of the intermetallic region to the reaction. It was verified that this property depends on overpotential, defining two ranges of positive excess values, 0.6 - 0.82 and 0.88 - 1.0, separated by the range 0.82 - 0.88, where the contribution of the boundary region is negligible. A simple model was developed, which explains the experimental results on the basis of the spillover of the adsorbed reaction intermediates, while the reaction between adsorbed species on both sides of the intermetallic edge is not feasible.Fil: Rau, Maria Sol. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Gennero, Maria Rosa. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Chialvo, Abel Cesar. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

Fast faradaic processes observed during the potentiodynamic polarization of polycrystalline palladium in acid electrolyte

Two almost reversible electrochemical systems are detected during the potentiodynamic anodization of polycrystalline palladium in 1 M H2SO4 and 1 M HClO4 by applying the triangular modulated triangular potential sweep technique. The first electrochemical system which appears in the 0.7–0.9 V range (vs. RHE) corresponds to the reaction Pd+H2O=PdOH+H++e− whose reversible potential is estimated as 0.80±0.02 V and the average half-life time of PdOH species is estimated as 6×10−3 s. The second electrochemical system appears when the anodizing potential sweep extends to the oxygen evolution potential region. The appearance of the second electrochemical system is accompanied by a change in colour of the electrode surface, a shift of the current-potential curve of the oxygen evolution reaction and an increase in thickness of the oxide anodic layer. The reversible response is tentatively assigned to the PdO2/PdO3 redox couple.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Changes in the polycrystalline gold electrode surface produced by square wave potential perturbations

The electroreduction of gold oxide layers produced by a square wave potential signal (SWPS) under a proper set of perturbation conditions yields a reproducible electrode surface with a large increase in the surface area. The different variables are systematically investigated to establish the optimal conditions of the SWPS. The results are discussed on the basis of the thermodynamics and kinetics of oxide monolayer and multilayer formation.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Changes in the electrochemical response of noble metals produced by square-wave potential perturbations : A new technique for the preparation of reproducible electrode surfaces of interest in electrocatalysis

A square-wave potential anodizing procedure to obtain noble metal surfaces with both a controlled roughness and a reproducible electrochemical response is presented. The influence of the characteristics of the square-wave potential perturbation are systematically studied. The modification of the surface takes place through the formation of a hydrated platinum oxide layer which is later electroreduced. The mechanism of growth of the hydrated oxide layer under both square-wave potential perturbation and potentiostatic conditions is critically discussed in terms of a complex sandwich-type structure.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Resolution of the mechanism of CO electrooxidation on steady state and evaluation of the kinetic parameters for Pt and Ru electrodes

The carbon monoxide oxidation reaction (COOR) was studied on steady-state conditions by chronoamperometry on polycrystalline smooth platinum and ruthenium rotating disc electrodes in CO-saturated acid solution. The chronoamperometric response did not show current oscillations and therefore the current density (j) vs. overpotential (η) curves on steady state could be obtained. In order to interpret these results, kinetic expressions were derived starting from the mechanism proposed by S. Gilman, which considers two adsorbed reaction intermediates, carbonmonoxide (CO ad) and hydroxyl (OH ad). Analytical expressions as a function of overpotential for the current density, the surface coverage of the adsorbed species (θ CO and θ OH) and the CO and CO 2 pressures at the electrode surface on steady state were obtained. This set of equations was used for the correlation of the experimental polarization curves and the evaluation of the corresponding kinetic parameters. From these values, the dependences of the surface coverage of the adsorbed intermediates on overpotential were simulated, as well as those of the partial pressure of CO and CO 2. Thus, it was demonstrated that the Gilman's mechanism accurately describes the experimental results on steady state of the COOR on these metals.Fil: Rau, Maria Sol. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: Gennero, Maria Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: Chialvo, Abel Cesar. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

Kinetic Study of the Hydrogen Oxidation Reaction on Membrane Coated Electrodes. Part I: Theoretical Aspects

A generalized theoretical analysis of the kinetics of the hydrogen oxidation reaction under the Volmer-Heyrovsky-Tafel mechanism on an electrode covered by polymeric films is presented. The treatment includes the diffusion of the molecular hydrogen through the electrolyte solution, as well as through the different layers and interfaces. On the light of the resulting expressions, the applicability of the Levich-Koutecky diagrams for the determination of the kinetic current densities was critically analyzed.Fil: Marozzi, Carlos Alberto. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: Gennero, Maria Rosa. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: Chialvo, Abel Cesar. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentin

Changes in the electrochemical response of noble metals produced by square-wave potential perturbations : A new technique for the preparation of reproducible electrode surfaces of interest in electrocatalysis

A square-wave potential anodizing procedure to obtain noble metal surfaces with both a controlled roughness and a reproducible electrochemical response is presented. The influence of the characteristics of the square-wave potential perturbation are systematically studied. The modification of the surface takes place through the formation of a hydrated platinum oxide layer which is later electroreduced. The mechanism of growth of the hydrated oxide layer under both square-wave potential perturbation and potentiostatic conditions is critically discussed in terms of a complex sandwich-type structure.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta