Electrochemical behaviour of phenylethanolamine at gold in aqueous solution

The electrooxidation of phenylethanolamine (2-amino-1-phenylethanol) at a gold electrode in alkaline electrolyte has been studied. Measurement of the differential capacitance of the electric double layer versus the electrode potential has shown that the adsorption of phenylethanolamine at the gold-solution interface plays a significant role in the oxidation mechanism. The effect of amine concentration, electrolyte pH and potential scan rate on the electrooxidation is analysed.     

Ageing and the diffusion process at the nickel hydroxide electrode

The ageing of α-Ni(OH)₂ causes changes in the characteristics of the electrode due to the formation of different oxyhydroxides on charging. The discharge process has been studied by potential step technique, and diffusion coefficients refined by extrapolation have shown little variation with ageing for measurements made at room temperature. An unusual temperature function has been recorded and its mechanistic implications are discussed.     

Voltage decay at passivated zinc anodes

A study has been made of the passivating process at a zinc electrode in KOH solutions. Zinc electrodes were passivated at a constant overpotential and the current response during passivation was measured. The potential response after the passivating potential was removed was also measured.The current during passivation soon reached a semi-steady-state value which increased with increasing overpotential but varied only slightly with changing KOH concentrations.When electrodes were passivated at overpotentials >325 mV, the open circuit voltage decay showed an arrest, the duration of which decreased with increasing KOH concentration. This duration increased when ZnO was dissolved in the electrolyte, when the temperature was decreased, and when the passivating overpotential was increased.The results are interpreted by assuming that passivation is due to the formation of a film, possibly Zn(OH)₂, which can dissolve in the electrolyte. The potential of the electrode is a mixed potential.     

Current distribution at electrode surfaces as simulated by finite element method

In this article, an approach of finite element method has been introduced to predict the distribution of potential and current on electrode surfaces. In this method, the bulk of electrolyte solution and the main body of solid electrodes are modeled to be normal conductive media; while the surface of the electrode, whose current-potential (I-V) curve satisfies experimental data, is modeled to be special nonlinear boundary conditions. This modeling approach for electrochemistry system is successfully verified by experimental data, and would contribute to a better understanding of the distribution of electrical potential and current at electrode surfaces in practical systems with high voltage coupling effect.     

Electropolymerization of phenol on a vitreous carbon electrode in alkaline aqueous solution at different temperatures

Electrochemical oxidation of phenol in basic aqueous solution has been studied on a vitreous carbon electrode at different temperatures in the range of 25-85 °C by cyclic voltammetry and chronoamperometry techniques. The electrochemical oxidation of phenol led to a complete deactivation of the electrode, whatever the temperature used, as a result of the deposition of an adhesive and insulating polymeric film. The electrochemical activity of the electrode was progressively restored by repeated potential scans in the range of water stability only when conducted at high temperatures; electrode reactivation was explained by an increase in the polymeric film permeability for both electrons (electron tunneling) and phenol molecules (diffusion). Chronoamperometric measurements carried out in the potential region of water stability have shown that electrode passivation was reduced or prevented at high temperatures. For chronoamperometry performed at the onset of oxygen evolution, the electrode remained active even at low temperatures because the discharge of water involved the production of hydroxyl radicals that destructively oxidized the polymeric film. The effect of temperature on electrode reactivation was determined by the measurement of current at an electrolysis time of 300 s; an increase of the temperature from 25 to 85 °C amplified the current from 0.212 to 5.373 mA.     

In situ FTIR spectra at the Pt electrode/γ-butyrolactone solution interface

The behavior of a Pt electrode/solution of lithium perchlorate and lithium hexafluorophosphate in a γ-butyrolactone (GBL) interface has been investigated by using in situ FTIR spectroscopy and single reflection ATR-FTIR spectroscopy. The bands due to free GBL and GBL solvated to lithium ions in the solution were confirmed by the single reflection ATR-FTIR spectra. The dependence of potential on the concentration of GBL and solvated GBL in the vicinity of a Pt electrode was investigated. In the FTIR spectra, the reversible changes in the concentration of free GBL and solvated GBL in the diffuse double layer were observed with change in potentials. As the potential decreased, the free GBL concentration increased, while the concentration of the GBL solvated to lithium ions decreased. The reverse phenomenon was observed as the potential increased. Thus, it can be concluded that the equilibrium shifts from Li⁺(GBL)₄ to Li⁺(GBL)₃ and GBL as the potential decreases. It became clear for low potentials that the product material contained lithium ions in irreversible reactions.     

The oxidation of trivalent chromium at the reconstructed Au(100) electrode

The electro-oxidation of Cr(III) to Cr(VI) species at the reconstructed Au(100) electrode has been investigated in a highly alkaline solution. The subsequent comparison of the results obtained with those at Au(111) electrode points to the structural sensitivity of this oxidation process related to different adsorbability of OH⁻ anions on both electrodes. Finally, it was found that the addition of Cr(III) ions does not shift the reconstruction peak to less positive values of potential indicating that for Au(100) electrode the oxidation process under consideration has no impact on the lifting of the surface reconstruction.     

Derivation of the explicit equation relating mass-transport-limited-current to voltage at the interface between two immiscible electrolyte solutions (ITIES)

The potential drop between two immiscible electrolyte solutions consists of the sum of that across the double layer and the diffusion barrier layer. A relation between these components has been proposed by Indenbom. We extended his approach to give a relation between the current density and the overall potential drop between the two bulk solutions. The final expression is mathematically similar to the Butler–Volmer equation for classical electrode kinetics.     

The electrochemistry of the tin oxide semiconductor—I. the establishment of mechanisms at polarized n-type tin oxide

The mechanisms of electrode potential re-establishment of the n-type unstoichiometrical tin oxide semiconductor electrode after cathodic and anodic polarization was investigated. The tin oxide semiconductor was polarized cathodically and anodically without evolution of hydrogen or oxygen and the potential/time curves at open circuit were observed. After cathodic polarization, the potential/time curve had one wave. The potential of this wave depended on the concentration and nature of the electrolytes, while its life-time depended on the imposed electrode charge. After anodic polarization, the potential/time curves did not show a similar wave.     

Kinetics of Ce(IV) reduction at gold,carbon and iridium electrodes

The characteristics of the cerium(IV) reduction have been examined at gold, glassy carbon and iridium rotating disk electrodes in 1 M sulphuric acid. Kinetic parameters have been evaluated from the reduction waves and are found to be independent of the electrode material. Cyclic voltammetric and radioactive measurements show that the adsorption of Ce(III) and Ce(IV) is extremely small or even nonexistent on all three electrode materials. The adsorption of oxygen at the electrode surface has only a small or negligible influence on the current—potential curves and the kinetic parameters.     

Investigation of the hydrogen evolution reaction at a 10 wt% palladium-dispersed carbon electrode using electrochemical impedance spectroscopy

The hydrogen evolution reaction (h.e.r.) at a 10 wt % palladium-dispersed carbon (Pd/C) electrode in 0.1 m NaOH solution has been investigated with reference to that on carbon (Vulcan XC-72) and palladium foil electrodes by analysing the a.c.-impedance spectra combined with cyclic voltammograms. From the coincidence of the maximum charge transfer resistances and the minimum hydrogen evolution resistances for the h.e.r. at the respective electrode potential for the Pd/C, carbon and Pd foil electrodes, it is suggested that the h.e.r. at the Pd/C electrode takes place along with the absorption and diffusion of hydrogen above –1.10 V vs SCE, whereas the former dominates over the latter below –1.10V vs SCE. In the case of the Pd foil electrode the transition of absorption and diffusion to evolution occurs at –0.96V vs SCE. In contrast to the Pd/C and Pd foil electrodes the h.e.r. occurs strongly at the carbon electrode below –1.20V vs SCE. The hydrogen evolution overpotential on the Pd/C electrode is decreased by 0.10 V in comparison to the carbon electrode due to the larger electrochemical active area of the finely dispersed Pd particles.     

Adsorption of triethanolamine at the solution/mercury and the solution/air interface

Comparison of adsorption of triethanolamine at the Hg/solution and the air/solution interface has been carried out by means of interfacial and surface tension and differential capacity measurements. Adsorption is stronger at the metal/solution interface than at the free surface of the solution. This is explained in terms of some metal—adsorbate specific interaction. Adsorption parameters for the Hg/solution interface indicate that the adsorbate molecules interact with neighbouring water molecules. While the flat orientation of the large organic molecule does not change with electrode charge, the functional OH groups, slightly turned to the solution, are very likely to rotate under the action of the electrode potential thus giving rise to a field dependent inner layer capacity, C₁.     

Hydrodynamic voltammetric studies of the oxygen reduction at gold nanoparticles-electrodeposited gold electrodes

The electrocatalytic reduction of oxygen at Au nanoparticles-electrodeposited Au electrodes has been studied using rotating disk electrode (RDE) voltammetry in 0.5 M H₂SO₄. Upon analyzing and comparison of the limiting currents data obtained at various rotation speeds of this RDE with those obtained at the bulk Au electrode, an effective value of the number of electrons, n, involved in the electrochemical reduction of O₂ was estimated to be ca. 4 for the former electrode and ca. 3 for the bulk Au electrode at the same potential of −350 mV versus Ag/AgCl/KCl(sat.). This indicates the higher possibility of further reduction and decomposition of H₂O₂ at Au nanoparticles-electrodeposited Au electrode in this acidic medium. The reductive desorption of the self-assembled monolayer of cysteine, which was formed on the Au nanoparticles-electrodeposited Au electrode, was used to monitor the change of the specific activity of the bulk Au electrode upon the electrodeposition of the Au nanoparticles.     

Fluctuations of concentration overpotential generated at gas-evolving electrodes

The electrode overpotential is usually expressed in terms of partial components related to ohmic, activation and concentration effects. For a gas-evolving electrode, the overpotential fluctuates because of bubble evolution but only the global overpotential fluctuations and, more recently, their ohmic part are easily accessible by routine experiments. In the present paper, high-amplitude fluctuations of concentration overpotential have been experimentally revealed by an anomalous behaviour of the current fluctuations induced by hydrogen evolution on platinum electrodes under potential control in alkaline media with or without the presence of a second mass-transport-controlled reaction. Inverted current jumps, reproducibly observed owing to an artificial bubble-nucleation site created on the edge of the rotating electrode, which provoked periodic bubble eruption, were ascribed to local concentration changes drastically affecting the current-lines distribution. These experimental results validate the theoretical models that predicted those anomalies but remained unverified up to now. A quantitative estimation of each overpotential component at bubble eruption is addressed by means of a simplified analytical approach supported by the simultaneous measurement of the electrochemical current noise and electrolyte resistance fluctuations.     

In situ FTIR spectra at the Cu electrode/propylene carbonate solution interface

In situ Fourier transform infrared spectroscopy (FTIR) spectra measurements were obtained for a Cu electrode/solution of lithium perchlorate in propylene carbonate (PC). The dependence of potential on the concentration of PC in the vicinity of the electrode was investigated. The bands due to free PC and PC solvated to lithium ions in the solution were distinguished by the single reflection attenuated total reflection (ATR) spectra. In the FTIR spectra, the reversible change in the concentration of free PC and solvated PC in the diffuse double layer was observed to be accompanied by a change in potential. As the potential decreased, the free PC concentration increased, while the concentration of the PC solvated to lithium ions decreased. Thus, it can be concluded that the equilibrium shifts from Li⁺(PC)₄ to Li⁺(PC)₃ + PC as the potential decreases. Furthermore, Li⁺(PC)₃ orientates itself so that it is parallel to the electrode surface.     

A reference electrode for electrochemical studies in fused alkali chlorides at high temperatures

A reference electrode based on the silver silver-chloride reaction has been developed for use in fused halide systems. The electrode

(i) Is reproducible to within better than ± 10 mV.

(ii) Remains constant in e.m.f. over long periods in fused alkali chlorides at 700°C and is unaffected by freezing and remelting of the electrolyte.

(iii) Does not contaminate the external melt, since the electrolyte junction is a glass sheath 1 mm thick.

(iv) Is robust and will even survive solidification of the melt.

Deviation from the Nernst equation has been found and is due to a junction potential across the glass sheath, for which quantitative corrections can be calculated. The transport number of the silver ion through Supremax glass in contact with solutions about 0.02 to 0.5 mole fraction of AgCl in an equimolar NaCl-KCl mixture is negligibly small at 700°C. A reference electrode with an electrolyte concentration of 0.271 AgCl mole fraction in an equimolar NaCl-KCl mixture has a potential of −939 mV with respect to the standard chlorine electrode at 700°C.     

The effect of experimental parameters on the rate and mechanism of oxidation of methanol at a platinum anode in aqueous acid

The oxidation of methanol on a platinum electrode in aqueous sulphuric acid has been studied further. It is shown that in addition to the normal parameters such as methanol concentration and potential, the mechanism of oxidation is critically dependent on the pretreatment of the platinum surface and the way in which the experiment is carried out (eg the period the electrode is in the double layer region before oxidation commences).     

Electrochemical oxidation of benzene at a glassy carbon electrode

Benzene oxidation in sulfuric acid at a glassy carbon electrode was investigated using voltammetric, chronoamperometric, and spectroscopic methods. The results are compared with those at a Pt electrode. Benzene was observed to be oxidized to benzoquinone presumably by active oxygen that was adsorbed on the GC electrode in the oxygen evolution region. It is concluded that oxidation at glassy carbon can produce benzoquinone or quinone-like compounds from an aqueous benzene solution. The applied potential for benzene oxidation should be less than 2.1 V vs RHE in order to prevent glassy carbon electrode damage by oxidation during long operation.     

Transient analysis of a flow-through porous electrode at the limiting current

The equations governing the transients in the concentration, current and potential response of a porous flow-through electrode at the limiting current for a single reactant in a well-supported electrolyte have been solved. It was assumed that a potentiostatic step was applied to an electrode with a uniform feed concentration. The dispersive flux of reactant was assumed to be negligible but double-layer charging effects were taken into consideration. If the double-layer time constant is much less than the fluid residence time (νC/?? ? 1), it is quantitatively shown that the capacitive current may be neglected in interpreting the current-time response of the electrode when examined in the fluid residence time frame. If the entire electrode is to operate at the limiting current, it is quantitatively shown that the solution phase ohmic drop can become significant early in the transient such that secondary reactions may become important. The ability to interpretI versust data in terms of the limiting current species mass transfer coefficient is removed under these conditions. The results support the qualitative arguments made by Newman and Tiedemann in their comprehensive review article on porous flow-through electrodes. Finally, it is shown that ln(Faradaic current) versust can be approximately linear in a limited time span, although no useful information can be obtained from such a plot.