Electrocatalytic Oxidation Of CO Research Articles

Synthesis of Pt–Ru@PThB catalyst by γ-irradiation and NaBH 4 as reducing agent

Pt–Ru particles were loaded onto spherical polythiophene balls (PThB) and new catalysts, Pt–Ru@PThBs, were prepared. Pt and Ru ions were subjected to chemical reduction using NaBH 4 as reducing agent or γ-irradiation in the presence of PThBs. The size, morphology, and composition of Pt–Ru@PThB catalysts were determined by transmission electron microscope (TEM), X-ray diffraction (XRD) and elemental analysis. TEM images of the Pt–Ru@PThB catalysts clearly provide evidences that Pt–Ru alloy nanoparticles are dispersed onto the surface of PThBs. The electrocatalytic efficiency of Pt–Ru@PThB was tested for electrochemical oxidation of carbon monoxide as well as for methanol. Pt–Ru@PThB catalyst prepared by γ-irradiation exhibits the enhanced electrocatalytic oxidation of CO and methanol. We envisage that Pt–Ru@PThB catalysts are suited for direct methanol fuel cells.

Direct Observation of Electrocatalytic Synergy

Here we describe an approach that directly and unambiguously establishes the synergistic effect between surfaces when brought into close proximity (Å's regime) through the use of a scanning tunneling microscope. As a model system, we have employed the electrocatalytic oxidation of CO chemisorbed onto a Pt(111) single-crystal electrode upon engaging a Ru tip. Not only have we been able to observe clear and compelling evidence of a synergistic effect, but also, this approach provides valuable mechanistic details not accessible from conventional measurements.

Electrocatalytic oxidation of CO on supported gold nanoparticles and submicroparticles: Support and size effects in electrochemical systems

We investigated the catalytic activity of gold particles toward CO electrooxidation by cyclic voltammetry and found that the formation of oxidic gold species on the surface of gold nanoparticles (AuNPs) is a necessary condition for electrooxidation of CO. The maximum potential in the positive-going sweep has a great effect on the formation of gold oxides as well as on the activity of AuNPs. We report the support-dependent electrooxidation of CO in aqueous solution as the first example of the contribution of the support to the high catalytic activity of AuNPs in electrochemical systems. We also show that particle size, reported to be a dominant factor in the catalytic oxidation of CO on AuNPs in solid–gas reaction systems, is no longer a critical factor controlling the activity of AuNPs in electrochemical systems. We demonstrate that indium tin oxide-supported gold submicroparticles, which are believed to be catalytically inactive due to their “large” size, exhibit surprisingly high activity toward electrooxidation of CO.

Electro-catalytic oxidation of CO on Pt catalyst supported on carbon nanotubes pretreated with oxidative acids

Characteristics of nanosized Pt electro-catalyst deposited on carbon nanotubes (CNTs) were studied with CO-stripping voltammogram and chronoamperometry measurements. The CNTs were pretreated by oxidation in HNO 3, mixed HNO 3 + H 2SO 4 and H 2SO 4 + K 2Cr 2O 7 solution, respectively, to enable surface modification. Well-homogenized Pt particles (average size: ≈3 nm) were loaded onto the pretreated CNT samples by a modified colloidal method. TEM, BET, FTIR and XRD techniques were used to characterize the physicochemical properties of the pretreated CNT samples. In the electro-oxidation of CO, all the Pt/CNT samples showed lower on-set as well as peak potentials than the conventional Pt/XC-72 electro-catalyst, indicating that the Pt/CNT samples were more resistant to CO poisoning and could be superior anode electro-catalyst for the proton exchange membrane fuel cells (PEMFCs). Moreover, we found that the pretreatment of CNTs in mixed HNO 3 + H 2SO 4 solution was very beneficial for the performance enhancement of Pt/CNT electro-catalyst; the catalyst obtained as such gave the lowest peak potential and the highest catalytic activity for the electro-oxidation of CO. Larger amount of oxygen-containing functional groups, higher percentage of mesopores, and higher graphitic crystallinity of the pretreated CNTs were considered crucial for the performance enhancement, e.g., by strengthening the interaction between Pt nanoparticles and the CNT support and enhancing the mass diffusion in the electro-chemical reaction.

A First-Principles Analysis of the Electrocatalytic Oxidation of CO over PtRu Alloys

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Efficient Electrochemical Conversion of Carbon Monoxide by Rhodium Octaethylporphyrin Adsorbed on Carbon Black

We have found efficient electrocatalytic removal of CO by rhodium octaethylporphyrin on carbon black at a wide potential range. Using carbon-supported rhodium octaethylporphyrin, we have separated the Rh(II) state participating reaction and the Rh(III) state participating reaction with CO. We have clearly demonstrated electrocatalytic CO oxidation by rhodium(III) porphyrin. The onset potential for CO oxidation is much lower than that for CO oxidation by conventional Pt/Ru catalysts and cobalt porphyrin.

Electrocatalytic oxidation of CO on Pt-modified Ru(0 0 0 1) electrodes

Various amounts of Pt were electrodeposited onto a Ru(0 0 0 1) electrode, and the kinetics of electrooxidation of CO was studied by cyclic voltammetry. Ru(0 0 0 1) covered with small amounts of Pt forming patches of 2D-monolayers exhibits only low activity if compared with the bare Ru(0 0 0 1) or Pt(1 1 1) electrodes. However, with high Pt coverages associated with 3D cluster deposits the reactivity is markedly enhanced and reaches a maximum at about 50% surface coverage and then decreases again. The results bear close resemblance to the properties of the reverse system, viz. Ru deposited onto Pt or even of Pt Ru alloys and are rationalized in terms of a bifunctional mechanism: CO adsorbed at Pt sites react preferentially with OH −-species formed at adjacent Ru sites, while reaction on either Pt or Ru sites alone is less facile.

Nonuniform Reaction Rates during CO and CO/H2 Oxidation on Coupled Pt Electrodes

The electro-catalytic oxidation of CO and CO/H2 mixtures on polycrystalline Pt has been investigated on two electrodes with controllable degrees of coupling strength by means of experiments and numerical simulations. With strong positive coupling, large differences between the currents of the two almost-identical electrodes arise in a range of potential. Experiments on CO oxidation were carried out in three different electrolytes; all three electrolytes support pattern formation to an extent in the following order: 0.05 mol/L sulfuric acid with saturated sodium sulfate > 0.05 mol/L sulfuric acid > 0.1 mol/L perchloric acid. Experiments with 2% CO/H2 mixtures also exhibit nonuniform states with coupling. Numerical simulations on CO electro-oxidation confirmed the experimental findings: the current differences occur due to a symmetry breaking both with identical electrodes (through a pitchfork bifurcation) and with electrodes with inherent heterogeneities (due to a formation of an isola). The nonuniform r...

A Thermogravimetric Study of Alakanethiolate Monolayer-Capped Gold Nanoparticle Catalysts

ABSTRACTThe application of molecularly-capped gold nanoparticles (1–5 nm) in catalysis (e.g., electrocatalytic oxidation of CO and methanol) requires a thorough understanding of the surface composition and structural properties. Gold nanoparticles consisting of metallic or alloy cores and organic encapsulating shells serve as an intriguing model system. One of the challenges for the catalytic application is the ability to manipulate the core and the shell properties in controllable ways. There is a need to understand the relative core-shell composition and the ability to remove the shell component under thermal treatment conditions. In this paper, we report results of a thermogravimetric analysis of the alkanethiolate monolayer-capped gold nanoparticles. This investigation is aimed at enhancing our understanding of the relative core-shell composition and thermal profiles.

Ru Decoration of Stepped Pt Single Crystals and the Role of the Terrace Width on the Electrocatalytic CO Oxidation

The influence of monatomic steps on the oxidation of adsorbed CO is examined using potentiodynamic and galvanostatic experiments. Galvanostatic experiments allow a better determination of the lowest possible oxidation potential than cyclic voltammetry. By comparing results on Pt(111), Pt(665), Pt(332), and Pt(755), we found that steps with a local (110) geometry are more active than those with a (100) geometry. Steps can be decorated by Ru, thus leading to surfaces with a known atomic arrangement of the components. During galvanostatic oxidation of adsorbed CO on such surfaces a second potential plateau is observed, the value of which depends on the density of steps. These transients suggest the existence of an electronic effect in addition to the widely accepted bifunctional mechanism: Due to the electronic effect, only CO in the neighborhood of Ru is destabilized, whereas CO adsorbed at more distant sites is not influenced and has to diffuse uphill to the reactive sites, leading to an apparently slow diffusion. In addition, the spillover effect according to the bifunctional mechanism lowers the height of the activation barrier for CO oxidation and therefore has an influence on all adsorbed CO.

Electrocatalytic oxidation of CO on Ru(0001) surfaces: The influence of surface disorder

Smooth and rough (created by argon ion sputtering) Ru(0001) surfaces were structurally characterized by reflection high energy electron diffraction (RHEED), and their activity in electrooxidation of CO in 0.1 M HClO4 solution was probed by cyclic voltammetry (CV). While the peak potentials of CO-oxidation on the smooth surface varied with the CO,OH-adsorbate composition (which changed in subsequent scans), these were markedly (∼0.3 V) lower with the rough surface. This difference is attributed to the varying properties of the Ru–O bond whose activation is considered to be rate-limiting. The enhanced activity of the rough surface is also reflected by the fact that the entire amount of adsorbed CO becomes completely oxidized during the first anodic scan, while with the flat surface at least three cycles are required.

Nuclear Magnetic Resonance and Voltammetry Studies of Carbon Monoxide Adsorption and Oxidation on a Carbon-Supported Platinum Fuel Cell Electrocatalyst

Nuclear magnetic resonance (NMR) spectroscopy has been used in conjunction with voltammetry to investigate the mechanism for the electrocatalytic oxidation of CO on a carbon-supported Pt fuel cell electrocatalyst in 2 M at ambient temperature. The states of adsorbed the conditions which give rise to them, and their oxidation pathways were investigated as a function of coverage and the working electrode potential of adsorption CO was adsorbed from the electrolyte at various fixed values of between 0 and 600 mV vs. RHE. Submonolayer coverages of were formed in two different ways, by adsorption for limited amounts of time and by partial oxidation of an initially saturated coverage. The coverage was then characterized via voltammetric oxidation and via NMR. Voltammetry data were analyzed qualitatively in terms of the number, shape, and position of oxidation peaks and quantitatively in terms of the total charge required to oxidize the coverage and the total number of catalyst sites occupied by the NMR spectra were analyzed qualitatively in terms of their lineshape and position and quantitatively in terms of their integrated intensity. These results have been utilized in the formulation of an overall model for the adsorption and oxidation of CO on Pt in an acid electrolyte at ambient temperature. Three distinct forms of are identified on the Pt electrocatalyst, a linear carbonyl, a bridged carbonyl, and a reduced carbonyl (a hydrogenated carbonyl requiring a three-electron transfer for complete oxidation to The relative populations of these three species are found to depend strongly on and to be substantially independent of coverage. Different oxidation behaviors are observed for different populations of the three species, suggesting that different oxidation reaction pathways are associated with the three states. © 2001 The Electrochemical Society. All rights reserved.

Monte Carlo simulations of a simple model for the electrocatalytic CO oxidation on platinum

A simple lattice-gas model for the electrocatalytic carbon monoxide oxidation on a platinum electrode is studied by dynamic Monte Carlo simulations. The CO oxidation takes place through a Langmuir–Hinshelwood reaction between adsorbed CO and an adsorbed OH radical resulting from the dissociative adsorption of water. The model enables the investigation of the role of CO surface mobility on the macroscopic electrochemical response such as linear sweep voltammetry and potential step chronoamperometry. Our results show that the mean-field approximation, the traditional but often tacitly made assumption in electrochemistry, breaks down severely in the limit of vanishing CO surface mobility. Comparison of the simulated and experimental voltammetry suggests that on platinum CO oxidation is the intrinsically fastest reaction on the surface and that CO has a high surface mobility. However, under the same conditions, the model predicts some interesting deviations from the potential step current transients derived from the classical nucleation and growth theories. Such deviations have not been reported experimentally. Furthermore, it is shown that our simple model predicts different Tafel slopes at low and high potential, the qualitative features of which are not strongly influenced by the CO mobility. The comparison of our simulation results to the experimental literature is discussed in some detail.

Size effects of ultrafine palladium particles on the electrocatalytic oxidation of CO

Effects of palladium particle size on the electrocatalytic oxidation of carbon monoxide in an acidic solution have been examined by the use of modeled catalyst electrodes ( Pd GC ) with a flat and dense glassy carbon substrate. The cyclic voltammetry showed that higher overpotential is needed to oxidize carbon monoxide on palladium with a decrease in the palladium particle size. With decreasing size of palladium particles the oxidation of carbon monoxide seems to shift from a one-electron-transfer controlled mechanism to a two-electron-transfer controlled one.

Oscillatory instabilities during formic acid oxidation on Pt(100), Pt(110) and Pt(111) under potentiostatic control. II. Model calculations

A kinetic model is developed for the electrocatalytic oxidation of formic acid on Pt under potentiostatic control. The model development proceeds stepwise via a simple model of the electrocatalytic CO oxidation. The full model consists of four coupled, nonlinear ordinary differential equations. The scanned and stationary current/outer potential (I/U) behavior, stationary current oscillations, two-parameter bifurcation diagrams and stirring effects are simulated using realistic model parameters. The numerical findings are found to be consistent with the experimental results given by Strasser et al. The model reproduces period-1 as well as mixed-mode oscillations. Furthermore, a mechanistic analysis of the model was performed: two suboscillators are identified whose characteristics allow a plausible interpretation of the observed dynamics. After a classification of the suboscillators into previously described categories, an attempt is made to identify the minimal mechanistic requirements for electrochemical current oscillations.

Structural effects in electrocatalysis A comparative study of the oxidation of CO, HCOOH and CH3OH on single crystal Pt electrodes

The electrocatalytic oxidation of CO, HCOOH and CH3OH is compared on Pt(100), Pt(110) and Pt(111) single crystals. The similarity of behaviour of CH3OH and CO on the three single crystal planes leads to the conclusion that the oxidation of both compounds involves CO-like intermediates. On the other hand, HCOOH behaves quite differently, particularly on Pt(100) and Pt(111) electrodes, i.e its oxidation involves different adsorbed intermediates, some of them being poisoning species formed in the hydrogen region.

Structural effects in electrocatalysis: A comparative study of the oxidation of CO, HCOOH and CH 3OH on single crystal Pt electrodes

The electrocatalytic oxidation of CO, HCOOH and CH 3OH is compared on Pt(100), Pt(110) and Pt(111) single crystals. The similarity of behaviour of CH 3OH and CO on the three single crystal planes leads to the conclusion that the oxidation of both compounds involves CO-like intermediates. On the other hand, HCOOH behaves quite differently, particularly on Pt(100) and Pt(111) electrodes, i.e its oxidation involves different adsorbed intermediates, some of them being poisoning species formed in the hydrogen region.