Anodic Oxygen-transfer Reactions Research Articles

The size effect of Pt nanoparticles: a new route to improve sensitivity in electrochemical detection of As(iii)

The size effect of Pt nanoparticles on detection of arsenic is clarified and the phenomenon is explained by anodic oxygen-transfer reactions and binding energy.

Aliphatic polyamine oxidation response variability and stability at boron-doped diamond thin-film electrodes as studied by flow-injection analysis

Previously it was shown that four different aliphatic polyamines can be quantitatively electrooxidized at boron-doped diamond thin film electrodes without derivatization or the use of pulsed voltammetric waveforms [Anal. Chem. 71 (1999) 1188; Anal. Chem. 69 (1997) 4041]. The flow injection analysis (FIA-EC) investigation (amperometric detection mode) of cadaverine (CAD), putrescine (PUT), spermine (SPM) and spermidine (SPMD), reported previously [Anal. Chem. 71 (1999) 1188], are updated herein with particular emphasis on the electrode response variability and stability. Most of the measurements were made with a film deposited from a 0.50% methane-to-hydrogen (C/H) volumetric ratio. In general, films deposited with C/H ratios near this value tend to possess the requisite physicochemical properties to support anodic oxygen transfer reactions. The electrode performance was evaluated in terms of the linear dynamic range, limit of quantitation, response variability and response stability. A linear dynamic range from 1.0 μM to 1.0 mM and a limit of quantitation of 1.0 μM or 20 pmol injected (S/N≥3) were found for CAD, PUT, and SPMD. For SPM, a linear dynamic range from 0.32 μM to 1.0 mM and a limit of quantitation of 0.32 μM or 6.4 pmol were observed. The response variability, as low as 2–4%, was observed which is vastly improved over previous results. The improvement was achieved by introducing a 3–6 min delay period between injections. The long-term response stability was good with no evidence for any progressive response attenuation or complete fouling by the reaction product, even though a solid deposit was observed to accumulate on the electrode surface with extended use. The deposit appears to partially reduce the active electrochemical area for polyamine oxidation and to decrease the overpotential for water discharge. Preliminary chromatographic results demonstrated the possibility of separating and detecting the polyamines by a simple reverse-phase scheme at constant applied potential.

A mathematical model for anodic oxygen-transfer reactions at Bi(V)-doped PbO2-film electrodes

Abstract An approximate model is developed to describe the voltammetric response for anodic O-transfer reactions at Bi(V)-doped PbO2-film electrodes (Bi–PbO2). Because the Bi(V) sites were found earlier to function for preadsorption of reactant in the anodic O-transfer reactions of cysteine, the model developed here includes reactant adsorption at Bi(V) sites in the Bi–PbO2 surface. The validity of the model is demonstrated on the basis of the voltammetric response obtained for DMSO in 1.0 M HClO4. Good agreement is obtained between predicted and observed values of half-wave potential (E1/2) as a function of the relative density of Bi(V) sites (ρ=ΓBi(V)/ΓPb(IV)) in Bi–PbO2 film electrodes configured as rotated disks. For low site densities (0.11≤ρ≤0.4), E1/2 is a linear function of ln(ρ/(1+ρ)2); however, for high site densities (0.4≤ρ≤0.84), E1/2 is a linear function of ln(1/(1+ρ)). Agreement is also demonstrated for E1/2 as a function of variations in the rotational velocity of these electrodes. The agreement of the proposed model with experimental data is concluded to be evidence for the importance of reactant adsorption in anodic O-transfer reactions at Bi(V) sites in these Bi–PbO2 electrodes.

Pulsed electrochemical detection of thiocompounds following microchromatographic separations

Pulsed electrochemical detection (PED) following microchromatographic separations has been applied to the determination of thiocompounds (e.g., methionine, cystamine, glutathione, glutathione disulfide) under typical reversed-phase conditions. Both reduced and oxidized thiol moieties are detected with high selectivity and sensitivity without the need of derivatization. The anodic responses of model thiol redox couples are shown to be based upon oxide-catalyzed anodic oxygen transfer reactions at noble metal electrodes. The mechanism of detection and optimization of PED waveform parameters are studied using cyclic and pulsed voltammetry at rotated disk electrodes. In a comparative study of pulsed amperometric detection (PAD) and integrated pulsed amperometric detection (IPAD), IPAD is determined to be better suited to manage the large oxide-formation (background) currents, which accompany the Faradaic signal of the analyte. IPAD results in more stable baselines, eliminates oxide-induced artifacts, and yields lower limits of detection. The higher frequency waveforms (1 Hz) needed to define the narrow peaks of microchromatographic separations and the fast scan rates (1000 mV s −1) of the IPAD waveform require the use of microelectrodes (≤ 1 mm), which exhibit reduced capacitance effects. Mass detection limits for thiocompounds are typically 0.2–3 pmole for microbore chromatography and 0.1-0.3 pmole for capillary liquid chromatography. The high selectivity of PED for thiocompounds reduces sample preparation and produces simpler chromatograms of complex mixtures, such as liver extracts.

Electrocatalysis of Anodic Oxygen‐Transfer Reactions: Acetate‐Doped Lead Dioxide Electrodes in Sulfuric Acid Media

Oxidations of dimethyl sulfoxide, toluene, and p‐xylene at pure electrodes were determined to be under extreme kinetic control with values of the apparent heterogeneous rate constant . However, a significant increase in was observed at acetate‐doped electrodes in 1M . X‐ray diffraction data indicated the films retained the slightly distorted rutile structure of the β‐form of the pure . Catalysis of the anodic discharge of to produce adsorbed hydroxyl radicals is concluded to account for the enhanced catalytic activity of the films for the anodic oxygen transfer reactions in .

Voltammetric response of dimethyl sulphoxide at gold electrodes modified by thin films of bismuth-doped lead dioxide

The anodic oxidation of dimethyl sulphoxide (DMSO) to DMSO 2 is representative of numerous anodic oxygen-transfer reactions that do not occur at appreciable rates at conventional anodes, e.g., nobel metals and carbon. However, useful voltammetric waves can be obtained at noble metal electrodes modified by thin films of electrodeposited, bismuth(V)-doped lead dioxide (Bi-PbO 2). Voltammetric data for anodic deposition with cathodic stripping of Bi-PbO 2 films are examined for gold rotated disk electrodes in 1.0 M HClO 4 containing Pb 2+ with Bi 3+. Evidence is shown that ultra-thin films (< ca. 1 μm) of a reduced oxide, designated “Bi-PbO”, remain on the Au substrate when thick Bi-PbO 2 films (> ca. 10 μm) are voltammetrically stripped under rapid potential scan. The ultra-thin films possess a larger atomic ratio of Bi/Pb than the original thicker films and, following reoxidation to Bi-PbO 2, they display greater catalytic activity. The effect is interpreted on the basis of mediation of the oxygen-transfer step.

ChemInform Abstract: Electrocatalysis of Anodic Oxygen Transfer Reactions: Oxidation of Cyanide at Electrodeposited Copper Oxide Electrodes in Alkaline Media.

AbstractCuO films are readily deposited on a rotating disk electrode (Pt/stainless steel) from alkaline solutions containing Na3Cu(CN)4.

Electrocatalysis of Anodic Oxygen Transfer Reactions: Oxidation of Cyanide at Electrodeposited Copper Oxide Electrodes in Alkaline Media

Films of copper oxide were readily deposited electrochemically on conductive surfaces from alkaline solutions containing copper (I, II) cyanide. The resulting electrodes showed catalytic activity for the anodic oxidation of CN− to CNO− in alkaline media. The half‐wave potential was pH dependent, indicating the involvement of OH− in the reaction mechanism. Electrocatalysis was concluded to occur by oxygen transfer mediation facilitated by formation of CuIIIsites in the surface. The deposited films were only loosely adherent to the substrates and were susceptible to chemical dissolution in the presence of excessively high CN− concentrations over a long time period (ca. 30 min).

Electrocatalysis of anodic oxygen-transfer reactions: alpha-lead dioxide electrodeposited on stainless steel substrates

Dense and uniform films of alpha-PbO2 were electrodeposited on the surfaces of various types of stainless steel. In strongly alkaline media, these films were found to be very stable and exhibited significant electrocatalytic activity for the oxidation of Cr(III) and CN−. In acidic media, alpha-PbO2 films deposited on type-416 stainless steel, which had been passivated by anodization in a phosphate solution, were relatively stable and exhibited catalytic activity for oxidation of Mn2+. Rate constants for the anodic oxygen-transfer reactions of Cr(III), CN− and Mn(II) were estimated from data obtained at rotated disk electrodes.

ChemInform Abstract: Electrocatalysis of Anodic Oxygen Transfer Reactions. Comparison of Structural Data with Electrocatalytic Phenomena for Bismuth‐Doped Lead Dioxide.

AbstractO2 evolution potentials (ηox) and rate constants (k) are measured for the anodic oxidation of Mn(II) and 2‐thiophene carboxylic acid at Bi‐doped PbO2 in 1.0M HClO4 and XRD and TEM results are reported for the PbO2 electrodes doped with varying amounts of Bi.

Electrocatalysis of Anodic Oxygen Transfer Reactions: Comparison of Structural Data with Electrocatalytic Phenomena for Bismuth‐Doped Lead Dioxide

X‐ray structural data, evolution overpotentials , and rate constants are compared for anodic oxidation of Mn(II) and 2‐thiophene carboxylic acid (2‐TCA) at Bi‐doped in . It is concluded that the rutile structure of pure deposited anodically from containing Pb(II) is retained even as the Bi(III) content is increased to , i.e., mole fraction . There is no evidence of a new oxide phase being formed. Crystallites of the are deposited with an increasing preferential orientation of the 020‐plane parallel to the Au substrate surface as the ratio Bi/Pb is increased. Increasing values of and decreasing values of appear to be correlated with the increased preferential orientation. However, change in preferential orientation is concluded not to be the primary determining factor in the electrocatalytic phenomena. The kinetic results are discussed also on the basis of the so‐called “volcano plot” of as a function of the enthalpy of transition between the two highest oxide phases for metal oxide electrodes.

Electrocatalysis of Anodic Oxygen Transfer Reactions: Detection of Soluble Intermediate Products during Electrodeposition and Stripping of β‐Lead Dioxide at a Gold Electrode

An Au rotated ring‐disk electrode (RRDE) was applied for the detection of soluble intermediate products during the anodic electrodeposition and cathodic dissolution of in solutions of . A soluble species which only can be reduced at the ring electrode is produced during the anodic nucleation and deposition processes for at the disk electrode. This soluble intermediate product is concluded to be Pb(IV) which is probably associated with oxygen, e.g., or . The cathodic ring current from detection of the soluble Pb(IV) species was studied as a function of the concentrations of Pb(II) and , and variation of rotational velocity. The results are consistent with chronamperometric data for deposition described previously. Soluble Pb(IV) and Pb(III), as well as Pb(II), are concluded to be products of the cathodic dissolution of .