Decrease In Overvoltage Research Articles

Effect of hydrophobicity on the hydrophobic-modified polytetrafluoroethylene/PbO 2 electrode towards oxygen evolution

The effects of hydrophobicity toward oxygen evolution in 1 M H 2SO 4 on the PbO 2 and polytetrafluoroethylene (PTFE)/PbO 2 electrode were elucidated in this study via an analysis of d.c. polarization and the a.c. impedance response together with the technique of atomic force microscopy (AFM). A marked decrease in overvoltage for the oxygen evolution reaction was observed on the hydrophobic-modified PTFE/PbO 2 anode when compared with a PbO 2 anode. The smaller electrochemically active area was indicated by the smaller value of both the electrochemically active surface area (charge Q*) and the capacitance C dl of the working electrode present on the hydrophobic PTFE/PbO 2 than on the PbO 2 electrode. Additionally, a smoother topology was also observed from the AFM to be present on the hydrophobic PTFE/PbO 2 than on the PbO 2 electrode. A higher relative rate for the oxygen evolution in 1 M H 2SO 4 on hydrophobic PTFE/PbO 2 than on PbO 2 was ascribed to both the bubble-removing effect caused by the hydrophobic centers and the fact that lower electrochemically active surface area for the anodic composite electrodeposition of PTFE/PbO 2 is compensated by the higher electrocatalytic activity of active sites under a high applied overvoltage. The electrochemical stability of the hydrophobic PTFE/PbO 2 anode was inferred to be substantially enhanced when compared with the unmodified PbO 2 anode. PbO 2 modified with the hydrophobic PTFE center via anodic composite electrodeposition resulted in a marked improvement in the electrocatalytic activity of the electrochemically active sites. An alteration of the surface structure of hydrophobic-modified PTFE/PbO 2 was also inferred from the observation of AFM image to be exhibited when compared with PbO 2.

Cholesterol sensor based on electrodeposition of catalytic palladium particles

A layer of palladium particles was electrodeposited on a glassy carbon electrode. The dispersed Pd particles resulted in a large decrease in overvoltage for the electrochemical oxidation of H 2O 2 down to +0.4 V vs. Ag/AgCl, based on which a new kind of cholesterol sensor was fabricated. Cholesterol oxidase was immobilized on the Pd-dispersed electrode by cross-linking with glutaraldehyde and a layer of poly( o-phenylenediamine) (PPD) film was electropolymerized on the enzyme layer. The sensor shows a linear response in the concentration range 0.05–4.50 mmol l −1 with a rapid response of less than 20 s. The polymer film can prevent interference from uric acid and ascorbic acid and also increases the thermal stability of the sensor. The sensor can be used for 200 assays without an obvious decrease in activity.

Electrocatalytic reduction of dioxygen by cobalt tetra(4-N N′N″-trimethylanilinium)porphyrin

Cobalt tetra(4-N N′N″-trimethylanilinium)porphyrin (CoTMAP) has been studied in aqueous solutions using cyclic voltammetry, differential pulse voltammetry as well as by RRDE and spectroelectrochemical methods. The CoIII/CoIITMAP couple dissolved in 0.05 mol dm–3 H2SO4 has a redox potential of +0.14 V. The λmax of the Soret band are 427 and 412 nm for CoIII and CoIITMAP, respectively. The rate constant for the reaction between CoIITMAP and dioxygen in 0.05 mol dm–3 H2SO4 was estimated to be 3 × 107 dm3 mol–1 s–1. The CoIIITMP has been found to absorb at monolayer levels on glassy carbon surfaces and to have a catalytic effect on dioxygen electroreduction in aqueous solutions. This catalytic effect is strongly dependent on electrolyte pH. The overvoltage of O2 reduction is reduced by 480 mV and insignificant amounts of H2O2 are produced at pH 1, while an overvoltage decrease of 300 mV and an H2O2 yield of 70% are observed at pH 8.

Hydrogen Overvoltage on Tin Self‐Cleaning Rotating Electrode (SRE) in Absence and Presence of Surface Active Ions

An investigation of hydrogen overvoltage on tin self‐cleaning rotating electrode (SRE) in sulfuric acid solution in the presence and absence of some halogen ions was carried out. It was established that the rate of the mechanical renewal exerts significant influence on the hydrogen evolution overvoltage decreasing it about 0.120V. It was found that the halogen ion adsorption practically does not change the magnitude of the overvoltage decrease which remains of the same order as it is in pure sulfuric acid. It was shown that the effective energy of activation of the hydrogen evolution process upon a continuously renewed surface decreases about two times in comparison with an unchanged surface.

High Rate Discharge Characteristics of Li / SOCl2 Cells

The performance characteristics of the cell have been determined as a function of discharge rate, electrolyte composition, cathode thickness, and cell temperature. Cells have been discharged at rates ranging from about 3 to nearly 300 mA/cm2. Cathodes with electrolyte solutions have contained either or , with the most efficient discharge characteristics being realized with and solutions. The use of pure dissolved in as the electrolyte results in substantially higher average discharge voltages and discharge capacities than can be achieved with cells containing the conventional electrolyte. With both electrolytes, however, the discharge capacity per unit cathode volume (the effective cathode utilization) decreases with increasing cathode thickness, the rate of decrease being greater the higher the discharge current density. Increasing cell temperature results in an improvement in cathode utilization and a decrease in overvoltage, again with both and electrolyte solutions.

On porosity-overvoltage correlation for carbon anodes in cryolite-alumina melts

The anodic overvoltage in aluminium electrolysis was studied by steady-state current/voltage measurements with carbon anodes of different porosities: vitreous carbon, which is a non-porous material, spectral graphite, which contains micropores and industrial baked carbon of 8–24% porosity ( P 1) due to pores larger than 7.5μm. Replacement of vitreous carbon with baked carbon was accompanied by a drastic decrease in overvoltage. For a given overvoltage, baked carbon yields a linear increase of cd with increasing P 1. It was established that the larger the P 1 parameter, the narrower is the range of Tafel behaviour, the lower are the Tafel slopes and the higher is the exchange current. These findings were interpreted in terms of reaction and diffusion overvoltage; their contribution depends directly on the porosity P 1. The higher P 1 for baked carbon, the larger is the diffusion overvoltage due to the diffusion into the anode pores.

Hydrogen evolution at mercury from acid concentrated aqueous solutions of indifferent salts

The possible reasons of the hydrogen overvoltage decrease at high supporting electrolyte concentrations have been considered. It follows from a comparative study of the kinetic isotope effect and overvoltage shifts that the overvoltage decrease cannot be ascribed to the Ψ 1 effect caused by the specific anion adsorption. The overvoltage decrease is associated with the discharge activation energy. It is suggested that in a high-concentration solution the hydroxonium ion is actually located in a different medium, which corresponds to a lower reorganization energy.

ChemInform Abstract: HOMOGENEOUS CATALYSIS OF CATHODIC REDUCTION OF OXYGEN IN COPPER‐CYSTAMINE AQUEOUS SOLUTIONS

AbstractBei der kathodischen Reduktion von O2 in sauerstoffgesättigten wässrigen Lösungen, die CuCl2 und Cystamin in äquimolarer Konzentration enthalten, nimmt aufgrund der katalytischen Wirkung des gebildeten Cu‐Cystamin‐ Komplexes die Sauerstoffüberspannung bei stationärer Stromdichte ab.

Homogeneous catalysis of cathodic reduction of oxygen in copper–cystamine aqueous solutions

The copper cystamine complex is a suitable system for the homogeneous catalysis of oxygen cathodic reduction in aqueous solutions. A steady state cathodic current density of 3.2 mA/cm2 at 0.2 V and an overvoltage decrease of 400 mV was observed in oxygen-saturated solutions of equimolar concentrations of CuII ions and cystamine (5 × 10–2 mol dm–3) at pH 4.5. For a given value of Cl– ion concentration and pH the catalytic current can be expressed by: Icat=k[CuII]0[O2].The optical, magnetic and kinetic properties of the catalyst were investigated. The results suggest that the CuII ion, although initially reduced to CuI, is stabilized by the disulphide bridge. It is also suggested that because the bridge is a two electron mediator for the reduction of oxygen, the potential barrier of the first electron reduction can be overcome.

Kinetics of hydrogen evolution and double layer structure on bismuth

A detailed quantitative study of hydrogen overvoltage on a bismuth electrode in solutions of HClO 4 has been carried out. Under conditions of sufficient purification, experimental Tafel curves are nonlinear over a wide range of potentials with the transfer coefficient α=0.61±0.01. Traces of oxygen in the solution cause a rapid decrease of overvoltage in the region of lower current densities. The form of the experimental Tafel curves and the magnitude of the dependence of overvoltage on pH and total concentration of electrolytes in the solution are in good quantitative agreement with the Frumkin theory of the slow discharge of hydroxonium ions. Specific features of the overvoltage decay on bismuth after the interruption of external current have been explained quantitatively on the basis of double layer effects.

Kinetics of hydrogen evolution and double layer structure on bismuth

Summary A detailed quantitative study of hydrogen overvoltage on a bismuth electrode in solutions of HClO 4 has been carried out. Under conditions of sufficient purification, experimental Tafel curves are nonlinear over a wide range of potentials with the transfer coefficient α=0.61±0.01. Traces of oxygen in the solution cause a rapid decrease of overvoltage in the region of lower current densities. The form of the experimental Tafel curves and the magnitude of the dependence of overvoltage on pH and total concentration of electrolytes in the solution are in good quantitative agreement with the Frumkin theory of the slow discharge of hydroxonium ions. Specific features of the overvoltage decay on bismuth after the interruption of external current have been explained quantitatively on the basis of double layer effects.

塩化ニッケル浴における添加剤の作用

Study was made on the inhibitor action of addition agents in the electrodeposition of nickel from nickel chloride bath.For the examination of the adsorption phenomena of the addition agents on the nickel surface, the capacity of double layer and the polarization potential during the hydrogen discharge on the nickel electrode in 0.1N HCl solution were measured with respect to the concentration of the addition agents.During the hydrogen discharge reaction, saccharin, thiourea, β-naphthoquinoline, and N-ethyl quinolium iodide reduced the differential capacity of double layer in 0.1N HCl solution.It was found that saccharin and thiourea decreased the overpotential of hydrogen discharge at lower concentrations. On the other hand, β-naphthoquinoline and N-ethyl quinolium iodide increased the overpotential, but gave rise to the lower limit of currents at higher concentrations in 0.1N HCl solution.The results would be explained by the strong adsorption of these compounds on the nickel cathode surface.Comparative study was made on the inhibitor action in terms of the increase or decrease of over-voltage (ΔE) due to the addition agents in the electrodeposition of nickel.The increase of ΔE was observed with the increase of current density by the addition of disodium 1.5-naphthalene sulfonate, thiourea, or coumarin (conc. of 2m M/l), but the decrease of ΔE was observed by the addition of butynediol under the same conditions.The addition of saccharin gave no change of ΔE at the current density of 0.5-50mA/cm2.