Oxygen reduction on carbon nanomaterial-modified glassy carbon electrodes in alkaline solution

Electroreduction of oxygen in alkaline solution on glassy carbon (GC) electrodes modified with different carbon nanomaterials has been studied. Electrochemical experiments were carried out in 0.1 M KOH employing the rotating disk electrode and rotating ring-disk electrode methods. The GC disk electrodes were modified with carbon nanomaterials using polytetrafluoroethylene as a binder. Four different carbon nanomaterials were used: multiwalled carbon nanotubes, carbon black powder, and two carbide-derived carbons (CDC). For the first time, the electrocatalytic behavior of CDC materials toward oxygen reduction is explored. Electrochemical characterization of the materials showed that all the carbon nanomaterial-modified GC electrodes are highly active for the reduction of oxygen in alkaline solutions.     

Electrochemical reduction of oxygen on double-walled carbon nanotube modified glassy carbon electrodes in acid and alkaline solutions

The oxygen reduction reaction has been investigated on double-walled carbon nanotube (DWCNT) modified glassy carbon (GC) electrodes in acid and alkaline media using the rotating disk electrode (RDE) method. The surface morphology and composition of DWCNT samples was examined by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Aqueous suspensions of DWCNTs were prepared using Nafion and non-ionic surfactant Triton X-100 as dispersing agents. The RDE results indicated that the DWCNT modified GC electrodes are active catalysts for oxygen reduction in alkaline solution. In acid media DWCNT/GC electrodes possess poor electrocatalytic properties for O₂ reduction which indicates lack of metal catalyst impurities in the DWCNT material studied. The oxygen reduction behaviour of DWCNTs was similar to that of multi-walled carbon nanotubes (MWCNTs) observed in our previous studies.     

Electrochemical study of the oxidation of tin(II) at glassy carbon electrodes

The voltammetric characteristics of the Sn(IV)/Sn(II) system have been studied at a glassy carbon rotating disk electrode in 4M hydrochloric acid. Anodic oxidation of Sn(II) produces a single well-defined wave, which has been examined in the temperature range 20-50 degrees , and shows distinct irreversibility. The kinetic parameters of the oxidation reaction have been calculated. Kinetic features of the reduction of Sn(IV) to Sn(II) were not evaluated because the reduction proceeds directly to tin metal.     

Electrochemical oxidation and determination of ceftriaxone on a glassy carbon and carbon-nanotube-modified glassy carbon electrodes

The electrochemical behavior of ceftriaxone was investigated on a carbon-nanotube-modified glassy carbon (GC-CNT) electrode in a phosphate buffer solution, pH = 7.40, and the results were compared with those obtained using the unmodified one [glassy carbon (GC) electrode]. During oxidation of ceftriaxone, an irreversible anodic peak appeared, using both modified and unmodified electrodes. Cyclic voltammetric studies indicated that the oxidation process is irreversible and diffusion-controlled. The number of electrons exchanged in the electrooxidation process was obtained, and the data indicated that ceftriaxone is oxidized via a one-electron step. The results revealed that carbon nanotube promotes the rate of oxidation by increasing the peak current. In addition, ceftriaxone was oxidized at lower potentials, which thermodynamically is more favorable. These results were confirmed by impedance measurements. The electron-transfer coefficients and heterogeneous electron-transfer rate constants for ceftriaxone were reported using both the GC and GC-CNT electrodes. Furthermore, the diffusion coefficient of ceftriaxone was found to be 2.74 × 10⁻⁶ cm² s⁻¹. Binding of ceftriaxone to human serum albumin forms a kind of electroreactive species. The percentage of interaction of ceftriaxone with protein was also addressed. A sensitive, simple, and time-saving differential-pulse voltammetric procedure was developed for the analysis of ceftriaxone, using the GC-CNT electrode. Ceftriaxone can be determined with a detection limit of 4.03 × 10⁻⁶ M with the proposed method.     

Electrochemical reduction of uranium(VI) in nitric acid-hydrazine solution on glassy carbon electrode

Electrochemical reduction of U(VI) in nitric acid-hydrazine solution is greatly influenced by the concentration of nitric acid. In low acidity nitric acid solution such as 0.1M (M=mol/dm³) HNO₃, U(VI) was firstly reduced to U(V) and then partially reduced to U(IV). In high acidity nitric acid solution, e.g., 3-6M HNO₃, an electrode process of two-electron transfer was involved in the reduction of U(VI). A higher U(IV) yield could be achieved in nitric acid solution with higher concentration. Hydrazine was very effective in suppressing the reduction of concentrated nitric acid, and the optimal concentration of hydrazine added was 0.075 to 0.15M in 6M HNO₃ This revised version was published online in July 2006 with corrections to the Cover Date.     

Cathodic reduction of coenzyme Q10 on glassy carbon electrode in acetic acid-acetonitrile solutions

The electrochemical reduction of coenzyme CoQ(10) and CoQ(0) on glassy carbon (GC) has been investigated in mixed solvent containing 80 vol.% acetic acid and 20 vol.% acetonitrile. A combination of cyclic voltammetry (CV) and rotating disk electrode technique (RDE) was employed to elucidate the mechanism of electrode processes. The results obtained were interpreted in terms of an E(r)E(q) mechanism involving the inverted ordering of formal potentials, i.e. E(2)(0')>E(1)(0'). The cathodic processes of both compounds consist of two successive one-electron one-proton steps, whereas the second electron transfer is thermodynamically more facile than the first. The processes occur with the generation of unstable semiquinone radicals as primary products. The results presented can help in explanation of the biochemical properties of CoQ(10) in the living cell.     

Oxygen reduction at the surface of glassy carbon electrodes modified with anthraquinone derivatives and dyes

The preparation, electrochemical and catalytic behaviour of glassy carbon electrodes modified by anthra-9,10-quinone, its amino derivatives and dyes were investigated. The stability of the modified electrodes was studied by cyclic voltammetry in acidic and neutral media. The electrocatalytic ability of the modified electrodes for the reduction of dioxygen to hydrogen peroxide was examined by cyclic voltammetry, chronoamperometry and chronocoulometry techniques. The influence of pH on the electrochemical and catalytic behaviour was studied and pH 5.0–8.0 was chosen as the optimum working pH by comparing the shift in oxygen reduction potential. The anthraquinone-adsorbed glassy carbon electrodes possess excellent electrocatalytic abilities for dioxygen reduction with overpotential ranging from 280 to 560 mV lower than that at a plain glassy carbon electrode. Hydrodynamic voltammetric studies were performed to determine the heterogeneous rate constants for the reduction of O₂ at the surface of the modified electrodes, mass specific activity of the anthraquinones used and the apparent diffusion coefficient of O₂ in buffered aqueous O₂-saturated solutions. Studies showed the involvement of two electrons in dioxygen reduction.     

抗坏血酸在聚阿魏酸修饰玻碳电极上的电化学行为研究

研究了抗坏血酸(AA)在聚阿魏酸修饰电极上的电化学性质。在AA存在的条件下,电极过程由扩散控制,测得扩散系数为8.18×10-8cm2/s。AA浓度在0.01~5.0 mmol/L范围内与峰电流呈现良好的线性关系。通过计时安培法测得催化速率常数为8.6×103mol-1.L.s-1。     

Electrochemical behavior of levodopa at multi-wall carbon nanotubes-quantum dots modified glassy carbon electrodes.

A multi-wall carbon nanotubes (MWNTs)-quantum dots (QDs) composite-modified glassy carbon electrode (GCE) was prepared. The complex was characterized by transmission electron microscopy (TEM). The electrochemical behavior of levodopa at MWNTs and QDs-modified GCEs (MWNTs-QDs/GCE) was studied by cyclic voltammetry (CV) and chronocoulometry (CC). It was found that its electrochemical behavior was a two-charge-two-proton process. The modified electrode had high electrocatalytic activity for levodopa with a standard heterogeneous rate constant of 0.595 cm s(-1), which was greatly increased compared with the values for bare GCE and individual MWNTs modified GCE. The better electrocatalytic activity for levodopa at MWNTs-QDs/GCE may due to a synergistic effect between MWNTs and QDs. This result provides a novel way to promote research on biomicromolecules at nano-dimensions.     

Oxygen reduction in acid media at the amorphous Mo–Os–Se carbonyl cluster coated glassy carbon electrodes

An amorphous Mo–Os–Se carbonyl cluster compound has been synthesized in 1,2-dichlorobenzene (b.p.≈180°C) to be tested as an electrocatalyst for molecular oxygen reduction in 0.5 M H₂SO₄. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) performed for the powder supported on pyrolytic carbon show a distribution of nanometer-scale amorphous particles with agglomerations in cluster forms. The catalytic activity was studied by the rotating disc electrode technique. Kinetic studies show a first-order reaction with a Tafel slope of −0.118 V dec⁻¹ and dα/dT=1.55×10⁻³ K⁻¹. In the temperature range 298–343 K, an activation energy of 32 kJ mol⁻¹ was determined.     

Electrochemical reduction of sulphur dioxide on inert electrodes in acetonitrile solutions

The reduction of SO₂ on Pt and glassy carbon electrodes in acetonitrile-0.1 M LiBr solutions is studied by chronopotentiometric and chronovoltamperometric techniques in a wide range of SO₂ concentrations. It is found that the reduction process involves an irreversible adsorption of the reaction products followed by a fast formation of a weakly soluble dithionate film which passivates the electrode surface. At sweep rates >0.1 V s^?1 the electric charge associated with cathodic reaction corresponds to that of a monolayer. The dependencies of the peak current and the peak potential on the sweep rate are in agreement with the requirements of the adsorption pseudocapacitance theory. The strong effect of water on the height of the cathodic peaks is indicative of the depassivation of the electrode by some active species formed in the presence of water, SO₂ and LiBr by a slow reaction.     

Electrocatalysis of oxygen reduction on glassy carbon electrodes modified with anthraquinone moieties

Anthraquinone groups were electrochemically grafted to glassy carbon (GC) electrodes via methylene linker to study the oxygen reduction reaction (ORR) in alkaline medium. Two different anthraquinone derivatives, 2-bromomethyl-anthraquinone or 2-chloromethyl-anthraquinone, were used to modify the GC electrode surface. Several modification conditions encompassing potential cycling and electrolysis at a fixed potential were employed in order to vary the surface concentration of MAQ groups (Γ _MAQ) and to study the dependence of the O₂ reduction behaviour on electrografting procedure. Cyclic voltammetry confirmed the presence of anthraquinone moieties attached to the GC electrode and Γ _MAQ varied in the range of (0.5–2.4)?×?10^?10 mol cm^?2. Oxygen reduction was studied on MAQ-modified GC electrodes of various surface coverage using the rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) methods. The RDE and RRDE results of O₂ reduction reveal that GC/MAQ electrodes show rather similar electrocatalytic behaviour towards the ORR yielding hydrogen peroxide as the final product.     

Electrochemical quartz crystal admittance studies of ion adsorption on nanoporous composite carbon electrodes in aprotic solutions

This paper describes the application of Electrochemical Quartz Crystal Admittance (EQCA) methodology to the tracking of ion adsorption on composite electrode coatings consisting of highly porous activated carbon particles and polyvinylidene difluoride (PVdF) binder rigidly attached to quartz crystal surfaces. Solutions of LiBF₄ and (C₂H₅)₄NBF₄ in propylene carbonate (PC) were used in this study. At small charge densities, the effect of frequency change is nearly of gravimetric nature. We propose a new method to determine the mass contribution to the resonance frequency shift due to adsorption of ions and accompanying solvent molecules, revealing different ion/solvent population ratios for Li⁺, (C₂H₅)₄?N⁺ and BF₄ ^? ions correlated to the ion solvation ability. The EQCA model applied describes the change in the frequency and in resonance peak width in terms of dimensional changes of large carbon particles (bumps) and of pseudo-uniform layers of smaller particles mixed with PVdF. The type of oscillation energy dissipation in composite carbon electrodes with PVdF binder strongly depends on non-uniform potential-induced deformations of electrode particles, and this suggests a strong effect of solvent nature on the mechanical properties of polymeric binders. EQCA may provide important information on the role of polymeric binders during cycling of composite electrodes both for supercapacitors and for Li-ion batteries electrodes.     

Electrochemical oxidation of benzaldehyde and hydroxybenzaldehydes in acetonitrile on platinum and glassy carbon electrodes

The electrochemical oxidation of benzaldehyde and four hydroxybenzaldehydes was studied on platinum and glassy carbon electrodes in acetonitrile. A considerable difference was observed in electrooxidation performed on platinum and glassy carbon electrodes. All hydroxy derivatives fouled the glassy carbon electrode, but platinum was passivated only by the electrooxidation of 3-hydroxybenzaldehyde, highlighting the crucial role of the position of the substituent relative to the hydroxy group. On the glassy carbon electrode, the formation of the corresponding benzoyl radical could have taken place, which promoted the buildup of polymers on the electrode surface.     

Oxygen reduction on polycobaltprotoporphyrin film: II. pH effect and the mechanism of oxygen reduction

The oxygen reduction kinetics on polycobaltprotoporphyrin (PCoPP) film has been examined with the rotating disc electrode technique in O₂-saturated solution of various pH. PCoPP film promotes the oxygen reduction process via two electrons to produce peroxide over wide pH range. When pH value of solution decreases, catalytic activity of PCoPP film increases. Possible catalytic mechanisms have been proposed for oxygen reduction.     

Electrochemical reduction of dioxygen on Alizarin modified glassy carbon electrode in acidic medium

The catalytic behaviour of glassy carbon electrode modified by 1,2-dihydroxy antraquinone (Alizarin) was investigated. The electrocatalytic ability of modified electrode for the reduction of dioxygen was examined by cyclic voltammetry and rotating disk electrode (RDE) voltammetry techniques. The Alizarin modified glassy carbon electrode possesses excellent electrocatalytic abilities for dioxygen reduction over potential 400 mV lower than at the bare glassy carbon electrode. Hydrodynamic studies were performed to determine the heterogeneous rate constant for the reduction of O₂ at the surface of modified electrode. It was determined by Koutecky-Levich plot. The apparent diffusion coefficient of O₂ in O₂ saturated acidic solutions was estimated by using Levich equation. Studies show the involvement of four electrons in dioxygen reduction at the surface of this modified electrode.     

Direct electrochemistry of catalase on glassy carbon electrodes.

Catalase was investigated as a possible catalyst of the electrochemical reduction of oxygen on glassy carbon electrodes. The presence of catalase dissolved in solution only provoked a moderate current increase, which was fully explained by the catalase-catalysed disproportionation of hydrogen peroxide (Scheme I). When catalase was adsorbed from dimethylsulfoxide on the surface of electrodes that did not undergo any electrochemical pre-treatment (EP), catalase efficiently catalysed oxygen reduction via direct electron transfer from the electrode (Scheme II). The results are discussed with respect to the electrode surface properties and the enzyme structure.     

Electrochemical behaviour of oxygen reduction on polymer carbon electrodes in alkaline media

The preparation of polymer carbon electrocatalysts by the controlled pyrolysis of polyfurfuryl alcohol polymer is described. The potentiostatic method was used to study the electrochemical behaviour of the oxygen reduction reaction on the prepared catalyst electrodes in potassium hydroxide electrolyte. A pure polymer carbon electrode and a cobalt chloride doped polymer carbon electrode were shown to be active in oxygen reduction, but the electrode containing cobalt chloride seemed the most active. The main reaction product at the pure polymer electrode is hydrogen peroxide, involving two electrons, whereas at a poly(CoCl₂) electrode the reduction process reaches partly its ultimate state, and involves at most three electrons.     

Electrochemical studies on lawsone and its determination in henna (Lawsonia inermis) extract using glassy carbon electrode

The electrochemical behaviour of lawsone at glassy carbon electrode (GCE) was investigated by using cyclic and differential pulse anodic stripping voltammetric (DPASV) techniques. Cyclic voltammetry was used to study the influence of pH on the peak current and peak potential. The Mcllavnie’s buffer of pH 3.0 was selected as a suitable analytical medium in which lawsone exhibited sensitive diffusion controlled redox peaks (vs. Ag/AgCl). The peak current varied linearly with lawsone concentration in the range between 0.60 and 1.40 μM with a detection limit of 6 nM. The applicability of the proposed method was illustrated by the determination of lawsone present in real samples. A mean recovery of lawsone in the leaf of Lawsonia inermis was 99.5% with a relative standard deviation of 1.15%.