Rotating Disk Electrode Voltammetry Research Articles

Understanding the electro-catalytic oxidation mechanism of urea on nickel electrodes in alkaline medium

In this paper, the electrocatalytic behavior of urea oxidation on a nickel electrode in alkaline medium was investigated using various electrochemical techniques: cyclic voltammetry (CV), linear sweep voltammetry (LSV), and rotating disc electrode voltammetry (RDE). Possible mechanisms have been proposed on the basis of the cyclic voltammetry data. The urea oxidation current shows a strong dependence on the concentration of urea and potassium hydroxide that enables the experimental determination, by Tafel studies, of the kinetic reaction orders for the oxidation of urea. The Tafel studies show reaction orders of 0.3 and 2, with respect to urea and OH− concentrations, respectively. The diffusion coefficient of urea was found to be 0.85×10−5cm2s−1. The presence of a mixed-controlled process (diffusion and kinetics) was confirmed for the oxidation of urea.

Electrochemistry of Room Temperature Protic Ionic Liquids: A Critical Assessment for Use as Electrolytes in Electrochemical Applications

Ten room temperature protic ionic liquids (RTPILs) have been prepared from low-molecular-weight Brønsted acids and amines with high purity and minimal water content, and their electrochemical characteristics determined using cyclic, microelectrode, and rotating disk electrode voltammetries. Potential windows of the 10 RTPILs were established at glassy carbon, gold, and platinum electrodes, where the largest potential window is generally observed with glassy carbon electrodes. The two IUPAC recommended internal potential reference systems, ferrocene/ferrocenium and cobaltocenium/cobaltocene, were determined for the 10 RTPILs, and their merits as well as limitations are discussed. Other electrochemical properties such as mass transport and double layer capacitances were also investigated. The potential applications of these RTPILs as electrolytes for electrochemical energy devices were discussed, and two novel applications using PILs for metal deposition and water electrolysis were demonstrated.

Effect of glycol-based coolants on the suppression and recovery of platinum fuel cell electrocatalysts

We use cyclic and rotating disk electrode voltammetry to study glycol-based coolant formulations to show that individual constituents have either negligible or significant poisoning effects on the nanoscale Pt/carbon catalysts used in proton exchange membrane fuel cells. The base fluid in all these coolants is glycol (1, 3 propanediol), commercially available in a BioGlycol coolant formulation with an ethoxylated nonylphenol surfactant, and azole- and polyol-based non-ionic corrosion inhibitors. Exposure of a Pt/Vulcan carbon electrode to glycol-water or glycol-water-surfactant mixtures causes the loss of Pt electrochemical surface area (ECSA), but the Pt ECSA is fully recovered in clean electrolyte. Only mixtures with the azole corrosion inhibitor cause irreversible losses to the Pt ECSA and oxygen reduction reaction (ORR) activity. The Pt ECSA and ORR activity can only be recovered to within 70% of its initial values after aggressive voltammetric cycling to 1.50 V after azole poisoning. When poisoned with a glycol mixture containing the polyol corrosion inhibitor instead, the Pt ECSA and ORR activity is completely recovered by exposure to a clean electrolyte. The results suggest that prior to incorporation in a fuel cell, voltammetric evaluation of the constituents of coolant formulations is worthwhile.

Application of the Surface Resistance Technique to Study the Metal|Polymer Interface: A Review Article

The use of surface resistance changes as an alternative method to study the metal|polymer interface is reviewed considering both experimental and theoretical aspects. The experimental arrangement in these investigations is, in general, one in which a polymer film is supported on a thin gold film, whose thickness is of the order of the mean free path of the conduction electrons (gold film thickness, φm ∼30 nm). Particular emphasis is laid on the effects of polymer thickness, electrolyte composition, degree of oxidation, and deactivation and reactivation processes of the polymer film on the metal film conductance. Relevant experiments, where the technique was employed to study the redox site distributions at the metal|polymer interface, during oxidation, deactivation and degradation of the polymer, were specially considered. The simple scattering model to explain surface resistance changes of a thin metal film coated with a poly(o-aminophenol) film is outlined on the basis of the specularity parameter, which represents the probability of an electron being reflected specularly or diffusely at the metal film surface. Information obtained by means of surface resistance is compared with that obtained by employing more traditional techniques such as cyclic voltammetry and rotating disc electrode voltammetry. Keywords: Degree of oxidation, Metal-polymer interface, Poly(o-aminophenol) films, Scattering model, Surface Resistance

Application of the Surface Resistance Technique to Study the Metal|Polymer Interface: A Review Article

The use of surface resistance changes as an alternative method to study the metal|polymer interface is reviewed considering both experimental and theoretical aspects. The experimental arrangement in these investigations is, in general, one in which a polymer film is supported on a thin gold film, whose thickness is of the order of the mean free path of the conduction electrons (gold film thickness, φm ∼30 nm). Particular emphasis is laid on the effects of polymer thickness, electrolyte composition, degree of oxidation, and deactivation and reactivation processes of the polymer film on the metal film conductance. Relevant experiments, where the technique was employed to study the redox site distributions at the metal|polymer interface, during oxidation, deactivation and degradation of the polymer, were specially considered. The simple scattering model to explain surface resistance changes of a thin metal film coated with a poly(o-aminophenol) film is outlined on the basis of the specularity parameter, which represents the probability of an electron being reflected specularly or diffusely at the metal film surface. Information obtained by means of surface resistance is compared with that obtained by employing more traditional techniques such as cyclic voltammetry and rotating disc electrode voltammetry. Keywords: Degree of oxidation, Metal-polymer interface, Poly(o-aminophenol) films, Scattering model, Surface Resistance

Simplifying the Evaluation of Graphene Modified Electrode Performance Using Rotating Disk Electrode Voltammetry

Graphene modified electrodes have been fabricated by electrodeposition from an aqueous graphene oxide solution onto conducting Pt, Au, glassy carbon, and indium tin dioxide substrates. Detailed investigations of the electrochemistry of the [Ru(NH(3))(6)](3+/2+) and [Fe(CN)(6)](3-/4-) and hydroquinone and uric acid oxidation processes have been undertaken at glassy carbon and graphene modified glassy carbon electrodes using transient cyclic voltammetry at a stationary electrode and near steady-state voltammetry at a rotating disk electrode. Comparisons of the data with simulation suggest that the transient voltammetric characteristics at graphene modified electrodes contain a significant contribution from thin layer and surface confined processes. Consequently, interpretations based solely on mass transport by semi-infinite linear diffusion may result in incorrect conclusions on the activity of the graphene modified electrode. In contrast, steady-state voltammetry at a rotating disk electrode affords a much simpler method for the evaluation of the performance of graphene modified electrode since the relative importance of the thin layer and surface confined processes are substantially diminished and mass transport is dominated by convection. Application of the rotated electrode approach with carbon nanotube modified electrodes also should lead to simplification of data analysis in this environment.

Electrocatalytic Hydrogen Evolution in Acidic Water with Molecular Cobalt Tetraazamacrocycles

A series of water-soluble molecular cobalt complexes of tetraazamacrocyclic ligands are reported for the electrocatalytic production of H(2) from pH 2.2 aqueous solutions. The comparative data reported for this family of complexes shed light on their relative efficiencies for hydrogen evolution in water. Rotating disk electrode voltammetry data are presented for each of the complexes discussed, as are data concerning their respective pH-dependent electrocatalytic activity. In particular, two diimine-dioxime complexes were identified as exhibiting catalytic onset at comparatively low overpotentials relative to other reported homogeneous cobalt and nickel electrocatalysts in aqueous solution. These complexes are stable at pH 2.2 and produce hydrogen with high Faradaic efficiency in bulk electrolysis experiments over time intervals ranging from 2 to 24 h.

Electronic Effects of Substituents on Redox Shuttles for Overcharge Protection of Li-ion Batteries

The redox behavior and kinetic parameters of five ferrocene derivatives were investigated in 1M LiPF6 in 50:50 volume percent EC:EMC, a typical electrolyte used in lithium-ion batteries. Using cyclic voltammetry (CV) and rotating disk electrode voltammetry (RDE) techniques, the effect of electron donating and withdrawing substituents on each derivative was evaluated from the view point of the Hammett substituent constant. We found that electrochemical rate constants of the ferrocene derivatives can be related to the Hammett equation which gives an accurate approximation for predicting the oxidation potential of redox shuttles when changes are desired in their electron donating and electron withdrawing properties by means of functional group substitution. Our results show that the exchange current density and reaction rate for oxidation decrease as the electron withdrawing property of the substituent increases. It is also shown that electron donating and electron withdrawing property of a substituent affect the exchange current density and electrochemical oxidation reaction rate obeying a trend opposite to that of the Hammett substituent constants (σ). The correlations found here are expected to improve the ability to systematically design chemical overcharge protection reagents through judicious substitution of functional groups on redox shuttles.

Electrocatalytic Reduction of Carbon Dioxide Using Pt∕C-TiO2 Nanocomposite Cathode

We show herein that Pt-modified carbon-titanium dioxide cathode nanocomposite matrices (designated hereafter as Pt/C-TiO2), prepared by heterogeneous photocatalysis, afford facile electrocatalytic reduction of carbon dioxide to methanol and isopropanol. Pyridinium cation was used as a solution co-catalyst in this study. The electrocatalytic activity of the new-generation Pt/C-TiO2 cathodes was quantitatively mapped by the combined use of rotating disk electrode voltammetry along with gas chromatography assay of the reduction products in solution.

Oxygen Reduction on Metal-Free Nitrogen-Doped Carbon Nanowall Electrodes

A plasma-enhanced chemical vapor deposition (PECVD) process using a CH4:H2 gas mixture creates vertically aligned carbon nanowalls (CNWs) on glassy carbon (GC) and Si substrates. Metal catalysts are not required for the nucleation and growth of CNWs on the substrates. The PECVD deposition temperatures and reaction times alter the morphology and thickness of the resulting CNW layer. A low-pressure, post-processing N2:Ar plasma treatment dopes the CNWs with nitrogen, and X-ray photoelectron spectroscopy measurements demonstrate that nitrogen is present at 4–20 atomic% with varying CNx bonding configurations dependent upon processing conditions. Raman spectroscopy shows relatively high intensity disorder bands (ID) compared to lower intensity graphitic bands (IG) indicating small crystalline domains. Rotating disk electrode voltammetry results show that the number of electrons (n) and kinetic current density (jk) of the oxygen reduction reaction both increase with nitrogen content. In addition, n and jk increase with thickness of the nitrogen-containing CNW deposit. The results indicate that nitrogen-doped CNWs have higher electrochemical reactivity than their non-doped counterparts.

Carbon-Supported Palladium Sub-Nanometer Particle Catalyst for Oxygen Reduction Reaction in Acid Media

Abstract Pd nanoparticles (Pd NPs) on a carbon support (Pd/C) were synthesized in ethylene glycol containing poly(1-vinyl-2-pyrrolidone) (PVP) at various PVP/Pd precursor ratios. The sizes of the Pd NPs were controlled by varying the PVP concentration. Smaller Pd NPs were obtained at higher PVP concentrations. Indeed, the mean sizes of the Pd NPs with PVP/Pd precursor ratios of 0, 40, and 80 (Pd/C-0, -40, and -80) were 2.8 (±1.2), 1.5 (±0.3), and 0.8 (±0.3) nm, respectively, by TEM analysis. The electrocatalytic activities of the Pd/C catalysts toward the oxygen reduction reaction (ORR) were examined in a 0.1 M HClO4 solution using rotating disk electrode voltammetry. The smaller Pd NPs exhibited more efficient ORR properties, such as a more positive ORR onset potential (or half-wave potential, E1/2) and increased number of electrons (n) transferred in the ORR. In particular, the Pd/C-80 catalyst with a lower metal content (7.9 wt % Pd) showed desirable ORR performance in terms of the onset potential, n value, mass activity, and methanol tolerance.

Microemulsion synthesis and electrocatalytic properties of carbon-supported Pd–Co–Au alloy nanoparticles

Carbon-supported Pd and Pd–Co–Au alloy electrocatalysts are prepared by water-in-oil microemulsion technique using water as aqueous phase, non-ionic Triton-X-100 as surfactant, and cyclohexane as oil phase. The materials are characterized using XRD, TEM, and EDX. Face-centered cubic structure of Pd and presence of respective elements with controllable composition is evident from the analysis of XRD and EDX. The role of alloying elements on the redox behavior as well as catalytic activity of Pd is studied by cyclic voltammetry and ultraviolet photoelectron spectroscopy. Electrochemical measurements performed by rotating disk electrode voltammetry indicate the good ORR activity of Pd–Co–Au/C compared to Pd/C.

Porous Pd Layer-Coated Au Nanoparticles Supported on Carbon: Synthesis and Electrocatalytic Activity for Oxygen Reduction in Acid Media

This paper reports the simple synthesis and characterization of carbon-supported Pd layer-coated Au nanoparticles (AuPd/C). A series of AuPd/C with various Pd/Au weight percentage ratios were prepared by the spontaneous deposition of a Pd shell on a Au nanoparticle core using different Pd precursor concentrations (0.5, 5, 10, 20 mM PdCl2). Au nanospheres encapsulated by the porous Pd shells are confirmed by transmission electron microscopy (TEM), UV–vis absorption spectroscopy, and scanning TEM. The catalytic activity of the AuPd/C for the oxygen reduction reaction (ORR) was investigated by rotating disk electrode voltammetry in 0.5 M H2SO4. In particular, a AuPd/C with a Pd/Au ratio of 0.61 shows superior ORR activity along with satisfactory stability and methanol tolerance under acidic conditions.

Mechanistic Discussion of the Oxygen Reduction Reaction at Nitrogen-Doped Carbon Nanotubes

The oxygen reduction reaction (ORR) at undoped and nitrogen-doped carbon nanotubes (CNTs and N-CNTs, respectively) was studied by cyclic voltammety, rotating disk electrode voltammetry, and gasometric analysis in neutral and alkaline aqueous solutions. At undoped CNTs, the ORR proceeds by two successive two-electron processes with hydroperoxide (HO2–) as the intermediate. At N-CNTs, the ORR occurs through a “pseudo”-four-electron pathway involving a catalytic regenerative process in which hydroperoxide is chemically disproportionated to form hydroxide (OH–) and molecular oxygen (O2). The ORR mechanism at both undoped and N-doped varieties is supported by steady state polarization and gasometric measurements of hydroperoxide disproportionation rates. An enhancement of over 1000-fold for hydroperoxide disproportionation is observed for N-CNTs, with rates comparable to the best known peroxide decomposition catalysts. A positive correlation between nitrogen content and ORR activities is observed where the ORR...

Electrochemical behavior and differential pulse voltammetric detection of thiobencarb on 2-(4-((4-ethoxyphenyl)diazenyl)phenylamino)ethanol-modified carbon paste electrode

Cyclic voltammetry, chronoamperometry, and rotating disk electrode voltammetry were used to investigate the electrochemical behavior of thiobencarb (TB) at carbon paste electrode modified with an azo dye, 2-(4-((4-ethoxyphenyl)diazenyl)phenylamino)ethanol (EDPE), EDPE/modified carbon paste electrode (MCPE). The modified electrode showed high electrocatalytic activity toward thiobencarb. The current was enhanced significantly relative to the situation prevailing when a bare glassy carbon electrode was used. The kinetics parameters of this process were calculated, the apparent electron transfer rate constant ks and α (charge transfer coefficient between electrode and EDPE) were 14.6 s−1 and 0.48, respectively. The experimental parameters were optimized, and the mechanism of the catalytic process was discussed. The best defined cathodic peak was obtained with 0.1 M acetate buffer (pH 3.0). The response of the sensor was very quick, and response time was approximately 5 s. The differential pulse voltammetry response of the MCPE was linear against the concentration of TB in the range of 0.96 to 106 μg L−1. The limit of detection was found to be 0.025 μg L−1. The precision was examined by carrying out eight replicate measurements at a concentration of 25 μg L−1 TB; the relative standard deviation was 2.9%.

Electrocatalytic reduction of nitrite on tetraruthenated metalloporphyrins/Nafion glassy carbon modified electrode

This paper describes the electrochemical reduction of nitrite ion in neutral aqueous solution mediated by tetraruthenated metalloporphyrins (Co(II), Ni(II) and Zn(II)) electrostatically assembled onto a Nafion film previously adsorbed on glassy carbon or ITO electrodes. Scanning electron microscope (SEM-EDX) and transmission electron microscopy (TEM) results have shown that on ITO electrodes the macrocycles forms multiple layers with a disordered stacking orientation over the Nafion film occupying hydrophobic and hydrophilic sites in the polyelectrolyte. Atomic force microscopy (AFM) results demonstrated that the Nafion film is 35 nm thick and tetraruthenated metalloporphyrins layers 190 nm thick presenting a thin but compacted morphology. Scanning electrochemical microscopy (SECM) images shows that the Co(II) tetraruthenated porphyrins/Nf/GC modified electrode is more electrochemically active than their Ni and Zn analogues. These modified electrodes are able to reduce nitrite at −660 mV showing enhanced reduction current and a decrease in the required overpotential compared to bare glassy carbon electrode. Controlled potential electrolysis experiments verify the production of ammonia, hydrazine and hydroxylamine at potentials where reduction of solvent is plausible demonstrating some selectivity toward the nitrite ion. Rotating disc electrode voltammetry shows that the factor that governs the kinetics of nitrite reduction is the charge propagation in the film.

Electrodeposited indigotetrasulfonate film onto glutaraldehyde-cross-linked poly- l-lysine modified glassy carbon electrode for detection of dissolved oxygen

The nano composited film of indigotetrasulfonate (ITS) electrodeposited onto poly- l-lysine (PLL)–glutaraldehyde (GA) (ITS/PLL–GA) was modified on glassy carbon electrode (GCE) by multiple scan cyclic voltammetry. Composited of the proposed film was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), electrochemical quartz crystal microbalance (EQCM), electrochemical impedance spectroscopy (EIS), and UV–vis spectrum for the absorption at λ max at 566 nm. For the electrocatalytic reduction of dissolved oxygen, ITS/PLL–GA film modified electrodes was determined in 0.1 M acetate buffer solution (pH 5.6) by cyclic voltammetry and rotating disk electrode voltammetry. This dissolved oxygen electrochemical sensor exhibited a linear response range (from 0 to 178.4 μM, R 2 = 0.9949), lowest detection limit (2.2 μM), lowest overpotential at −0.09 V, high sensitivity (906 μA mM −1) and relative standard deviation (RSD) for determining dissolved oxygen ( n = 3) was 4.2%. In addition, the ITS/PLL–GA/GCE was advantageous in terms of its simple preparation, specificity, stability and the ability of regeneration.

The contribution of low‐affinity transport mechanisms to serotonin clearance in synaptosomes

Although many studies assert that the serotonin (5-HT) transporter (SERT) is the predominant mechanism controlling extracellular 5-HT concentrations, accumulating evidence suggests that low affinity, high capacity transport mechanisms may contribute more to 5-HT clearance than previously thought. The goal of this study was to quantify the contributions of SERT relative to other mechanisms in clearing extracellular 5-HT concentrations ranging from 50 nM to 1 μM in synaptosomes prepared from wild-type and SERT knockout mice using rotating disk electrode voltammetry. SERT inhibitors combined with decynium-22 (D-22), a blocker of several low-affinity transporters, blocked all uptake of 5-HT into synaptosomes. We found that SERT is responsible for the majority of synaptosomal uptake only at relatively low 5-HT concentrations, but comprises a diminishing proportion of 5-HT clearance when extracellular 5-HT increases above 100 nM. The effect of D-22 was similar in wild-type and SERT knockout synaptosomes. Thus, there was no evidence of upregulation of low-affinity mechanisms in knockout mice across the concentrations of 5-HT tested. These are surprising results, in light of the prevailing view that SERT is the primary uptake mechanism for extracellular 5-HT at physiological concentrations. We conclude that non-SERT mediated 5-HT uptake is substantial even at modest 5-HT concentrations. These findings, in conjunction with other studies, have important implications for understanding serotonergic disorders and may explain the variable efficacy and stability of patients' responses to antidepressants, such as the selective serotonin reuptake inhibitors.

Electro-oxidation of BH4− in dimethylsulfoxide and dimethylformamide studied by rotating disk electrode voltammetry

Borohydride (BH4−) is a promising new fuel for fuel cells, yet its practical implementation has been hindered by a deleterious hydrolysis reaction to form H2 in aqueous solvents, especially at the high BH4− concentrations necessary for high-power fuel cells. We investigated a wide array of nonaqueous solvents for their ability to hold BH4− at higher concentrations and allow effective electro-oxidation at Pt and Au, two well-studied BH4− anode materials. Only dimethylsulfoxide and dimethylformamide were found to be suitable, and precluded BH4− decomposition to H2 in bulk solution (hydrolytic or otherwise). BH4− decomposition at electrode surfaces was still observed, however. Current densities in these solvents were about an order of magnitude below those observed in aqueous solution, and onset potentials were 0.7V less favorable. MeOH addition, to stabilize oxidized states of boron, did not increase current.

Reactivity of one-, two-, three- and four-electron reduced forms of α-[P2W18O62]6− generated by controlled potential electrolysis in water

One, two, three and four electron reduced forms of α-[P2W18O62]6− in aqueous acidic electrolyte media have been selectively generated by bulk electrolysis from a solution that has an initial pH of 3.6. The reactivities of the reduced polyoxometalate anions and identities of products formed in the presence and absence of dioxygen have been assessed via oxygen and hydrogen Clark-type electrodes, a pH electrode and rotating disk electrode voltammetry. [P2W18O62]7− is stable to protons but is slowly oxidized by dioxygen (timescale: hours to days) back to [P2W18O62]6−. In contrast, [P2W18O62]8− reacts more rapidly with O2 and slowly with H+, whereas generation of the [P2W18O62]9− and [P2W18O62]10− anion is accompanied by a large increase in pH and rapid reaction with O2 or, in its absence, with H+. Consequently, it is concluded that photocatalytic reactions based upon [P2W18O62]6− chemistry are only likely to be of significance if [P2W18O62]9− or more highly reduced species are generated and form part of the catalytic cycle.