New Type of an Adsorption Layer of Organic Molecules with a Cage Structure Condensed at the Electrode/Solution Interface: The Adsorption of Cubane Derivatives on a Mercury Electrode

A synthesis and a study by method of measuring the differential capacitance on a stationary mercury drop of the adsorption of a number of cubane derivatives in a surface-inactive electrolyte are performed. It is established that the compounds studied exhibit a high surface activity. For bromine derivatives of cubane (4-bromomethoxycarbonylcubane, 4-bromohydroxymethylcubane) the formation of two-dimensional adsorption layers is discovered. Values of adsorption parameters for these compounds are evaluated with use made of the Frumkin isotherm.     

Effect of Adsorption of Neutral Molecules on the EDL Capacitance of a Rough Electrode

The perturbation theory is used to design a theoretical model for the Frumkin–Melik-Gaikazyan impedance of a sine electrode with a perturbation parameter equal to the ratio between the amplitude of surface oscillations and its period for a diffusion-controlled adsorption stage. The unequal diffusion access to the interface increases its capacitance. At higher frequencies, the electrode capacitance is defined by its geometric roughness factor. At lower frequencies, the capacitance depends on the adsorption conditions. The adsorption of electroactive substances results in a constant phase angle; the electrode roughness alters it and the frequency range where it remains constant.     

Impedance Response of a Thin Film on an Electrode: Deciphering the Influence of the Double Layer Capacitance

The different contributions of the interfacial capacitance are identified in the case of passive materials or thin protective coatings deposited on the electrode surface. The method is based on a graphical analysis of the EIS results to determine both the passive-film capacitance in the high-frequency domain and the double-layer capacitance in the low-frequency domain. The proposed analysis is shown to be independent of the physicochemical origins of the frequency dispersion of the interfacial capacitances which results, from an analysis point of view of the experimental results, in the use of a constant-phase element However, for a correct evaluation of the thin-film properties such as its thickness, the high-frequency data must be corrected for the double-layer contribution. In particular, it is shown that if the double-layer capacitance gives a frequency-dispersed response, it is necessary to correct the high-frequency part for the double-layer constant-phase elements. This is first demonstrated on synthetic data and then used for the determination of the thickness of thin oxide film formed on Al in neutral pH solution.     

Unravelling Hydrogen Adsorption Kinetics on Ir(111) Electrode in Acid Solutions by Impedance Spectroscopy

The kinetics for hydrogen (H) adsorption on Ir(111) electrode has been studied in both HClO\begin{document}$ _4 $\end{document} and H\begin{document}$ _2 $\end{document}SO\begin{document}$ _4 $\end{document} solutions by impedance spectroscopy. In HClO\begin{document}$ _4 $\end{document}, the adsorption rate for H adsorption on Ir(111) increases from 1.74\begin{document}$ \times $\end{document}10\begin{document}$ ^{-8} $\end{document} mol\begin{document}$ \cdot $\end{document}cm\begin{document}$ ^{-2} $\end{document}\begin{document}$ \cdot $\end{document}s\begin{document}$ ^{-1} $\end{document} to 3.47\begin{document}$ \times $\end{document}10\begin{document}$ ^{-7} $\end{document} mol\begin{document}$ \cdot $\end{document}cm\begin{document}$ ^{-2} $\end{document}\begin{document}$ \cdot $\end{document}s\begin{document}$ ^{-1} $\end{document} with the decrease of the applied potential from 0.2 V to 0.1 V (vs. RHE), which is ca. one to two orders of magnitude slower than that on Pt(111) under otherwise identical condition. This is explained by the stronger binding of water to Ir(111), which needs a higher barrier to reorient during the under potential deposition of H from hydronium within the hydrogen bonded water network. In H\begin{document}$ _2 $\end{document}SO\begin{document}$ _4 $\end{document}, the adsorption potential is ca. 200 mV negatively shifted, accompanied by a decrease of adsorption rate by up to one order of magnitude, which is explained by the hindrance of the strongly adsorbed sulfate/bisulfate on Ir(111). Our results demonstrate that under electrochemical environment, H adsorption is strongly affected by the accompanying displacement and reorientation of water molecules that initially stay close to the electrode surface.     

Diffusion,Adsorption and Electrode Kinetics of Electro‐oxidatons on a Stationary Solid Electrode

The i‐E oxidation curves, obtained using a boron doped diamond electrode, for studies of oxidations of two piperazine derivatives ARIP (I) and PIRI (II), resulted in a sharp increase of current in the range of the oxidation potentials. After reaching a value, depending on concentration of I or II, the current remains practically constant up to +1.6 V. Such limiting currents i₁ are a linear function of concentrations and depend on the v^1/2. Hence it is diffusion controlled, shifts of the oxidation potentials indicate, that the monoprotonated forms are oxidized. At more negative potentials a limiting current i₂ occurs, due to the oxidation of the diprotonated form. Current i₂ increases with decreasing pH in a shape of a part of a dissociation curve. Diffusion control reflects the large size of molecules I and II. The two‐electron oxidations yield a C=N bond in the piperazine ring. It seems to be the first reported diffusion controlled oxidation curves obtained on a stationary solid electrode.     

Electrical Double Layer Structure on Electrodes of Platinum Metals: Effect of the Carbon Monoxide Adsorption

Results on the paper's theme are reviewed. Attention is focused mainly on the use of transients of current and open-circuit potential for elucidating changes in the structure of the electrical double layer (EDL) caused by the CO adsorption. It is shown that the high binding energy of CO with surfaces of platinum metals leads to a strong suppression of the total differential capacitance of the electrode, the recharge of the surface, the displacement of strongly adsorbed atoms formed during the adsorption of ions with a total charge transfer, and to other alterations in the EDL plates facing both solution and metal. The importance of allowing for double-layer effects when solving problems of electrocatalysis on platinum metals is emphasized.     

Pt(111)单晶电极上乙二醇解离吸附反应动力学

运用电化学循环伏安和程序电位阶跃方法研究了乙二醇在Pt(111)单晶电极上的解离吸附过程.动力学研究的定量结果指出,乙二醇解离吸附反应的平均速率随电极电位变化呈火山型分布,其最大值在0.10 V(vs SCE)附近.测得在含2×10－3 mol•L－1乙二醇的溶液中,最大初始解离速率vi为4.35×10－12 mol•cm-－2•s－1.     

低信膜比条件下金膜电极电位溶出分析法研究

推导并验证了信号与金膜厚度的比值较小（即低信膜比）时金膜电极电位溶出分析法的过渡时间方程式和电位时间方程式。实验确定的理论式的应用条件为τ／ｌ２≤５８×１０１０ｓ／ｃｍ２，并发现当扩散路径约为扩散层厚度的３倍时，便可按半无限扩散条件处理扩散问题。从而解决了利用小信号进行金膜电极电位溶出基本问题，即信号与浓度的定量关系。     

Specific Features of the Initial Stages of Oxidation of a Silver Electrode in Weakly Acidified Solutions of Sodium Fluoride

The behavior of a silver electrode, which is renewed in situ by mechanical cutting, in weakly acidified sodium fluoride solutions is studied with the aid of an impedance method and a method of cyclic voltammetry. The application of said procedures makes it possible to record time effects, which reflect the processes of electrochemical adsorption of oxygen at the interface between the silver electrode and the solution, in the potential region extending from −0.7 to 0.2 V (SCE). Approximate calculations of the effect of potential and the time of the electrode’s exposure (after its renewal) in contact with the electrolyte at given values of potential on the amount of adsorbed oxygen are performed on the basis of an analysis of the obtained experimental data. A comparison of the obtained results with the literature data makes it possible to put forth a substantiated opinion as to the reasons for the substantial difference in the intervals of potentials of ideal polarizability of the silver electrode/solution of a surface-inactive electrolyte system, which are presented in works of various authors.__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 857–865.Original Russian Text Copyright © 2005 by Safonov, Choba, Oshkin.     

Spillover on a Platinum Electrode Modified by MWNTs

The spillover phenomenon is observed on the platinum (Pt) disk electrode modified by multi-wall carbon nanotubes (MWNTs). The rate of the spillover of oxygen-containing species produced on Pt surface to and from MWNTs is fast. However for hydrogen-adatoms, the spillover is very weak. The selective spillover on the Pt/MWNTs electrode may provide a novel way to design catalysts.     

阴离子特性吸附和Pt(111)电极表面结构对乙二醇解离吸附动力学的影响

运用电化学循环伏安和程序电位阶跃方法研究了阴离子特性吸附和Pt(111)电极表面结构对乙二醇解离吸附反应动力学的影响. 结果表明, 阴离子特性吸附显著影响乙二醇的解离吸附, 在高氯酸介质中(无特性吸附)测得乙二醇解离吸附反应的初始速率vi以及解离吸附物种(DA)的饱和覆盖度均明显大于硫酸溶液(发生SO2-4/HSO-4特性吸附)中的相应值; 其平均速率v随电极电位的变化呈类似火山型分布, 最大值位于0.22 V(vs SCE)附近. 还发现通过不同处理获得的Pt(111)电极的不同表面结构对这一表面过程也具有显著的影响.     

Adsorption from a Layer of Finite Thickness on a Planar Electrode

Within the Nernst diffusion model, the effect the convection has on the adsorption at a planar electrode is studied for the case of a diffusion-controlled stage of adsorption and the behavior of the Frumkin–Melik–Gaikazyan finite adsorption impedance is analyzed. Allowing for the convection leads to new functional frequency dependences of constituents of this impedance at low frequencies, where the active constituent depends on the diffusion layer thickness more heavily than the capacitive one. During adsorption of neutral molecules from a layer of finite thickness, an additional relaxation time emerges in an electrochemical system, which results from a finite rate of motion of species in the near-electrode layer. Ignoring the convection may lead to erroneous interpretation of the adsorption mechanism.     

Effect of Inorganic Ions on Oleate Adsorption at a Nigerian Hematite–Water Interface

Using “pure” natural hematite selected from a high silica Nigerian hematitic ore, oleate adsorption densities at the hematite–water interface were determined in the presence of various inorganic ions (anions and cations) of different charges and at varying concentrations. Adsorption density was determined using electrical conductivity measurements. The specific surface area of the hematite particles was determined using the method of adsorption of paranitrophenol in aqueous solution. Inorganic ions in solution depressed oleate adsorption at the aqueous hematite surface. The charge of the ion proved to be the dominant factor determining the depression of oleate adsorption. Ionic strength also was an influence, up to a limiting value at which monolayer oleate coverage of the hematite surface occurred. The inorganic ions in solution are considered to function through nonspecific adsorption in the diffuse region of the electric double layer.     

A Simulation of an Anion‐Induced Adsorption of Metal Ions in Pseudopolarography Using a Thin Mercury Film Covered Rotating Disk Electrode

A theory of the influence of anion‐induced adsorption of metal ions in pseudopolarography using the thin mercury film covered rotating disk electrode is developed. The model is developed assuming that the metal ion is forming several labile complexes with the ligand which is present in a great excess, and that only one complex species is adsorbed following a linear isotherm. The results obtained assuming steady‐state conditions are compared with the simulation of transient processes using Galerkin and finite difference methods. It is shown that the adsorption of metal complexes on the disk electrode surface does not prevent the determination of the stability constants.     

金电极基本性质的研究综述

该文从金电极的电化学行为影响因素、阴离子表面吸附和电极面积求算3个方面对金电极的基本性质进行了综述.金电极基本性质的探讨对于相关领域的研究具有重要的指导意义.     

Electrochemical Studies of the Benzoate Adsorption on Au (111) Electrode

Cyclic voltammetry (CV), differential capacity (DC), and charge densitymeasurements have been employed to study the benzoate (BZ) adsorption at the Au(111)electrode surface. Thermodynamic analysis of charge density (_M) data has beenperformed to describe the properties of the adsorbed benzoate ion. The Gibbsexcess , Gibbs energy of adsorption G, and the number of electrons flowingto the interface per adsorbed benzoate ion at a constant potential (electrosorptionvalency) and at a constant bulk concentration of the benzoate (reciprocal of theEsin—Markov coefficient) have been determined. The results demonstrate thatalthough benzoate adsorption starts at negative charge densities, it takes placepredominantly at a positively charged surface. At the most positive potentials,the surface concentration of benzoate attains a limiting value of about 7.3×10^–10mol-cm^–2, which is independent of the bulk benzoate concentration. This valueis consistent with packing density corresponding to a closed-packed monolayerof vertically adsorbed benzoate molecules. At negative charge densities, benzoateassumes a flat (-bonded) surface coordination. The surface coordination ofbenzoate changes, by moving from a negatively to positively charged surface.At the negatively charged surface, the electrosorption bond is quite polar. Thepolarity of the chemisorption bond is significantly reduced due either to a chargetransfer or a screening of the charge on the anion by the charge on the metal.     

由扩散阻抗过渡区求金属氢化物电极中氢扩散系数的不确定性(英文)

本文参照文献[1] 报导的利用扩散阻抗过渡区求金属氢化物电极中氢扩散系数的方法测定了MlNi3.75Co0 .6 5Mn0 .4 Al0 .2 电极中氢的扩散系数 .结果发现 :运算过程中由于所用到的一些函数具有周期性 ,使计算结果变为多解 ,而且这些解之间存在着数量级上的差别 ;对同一组实验数据 ,过渡区内依据不同频率点求得的扩散系数也很不同 .总之 ,该方法尚不成熟 ,有待于进一步完善     

EQCM Study of the Couple Thallium(I)/Thallium Amalgam at a Thin Film Mercury Electrode

EQCM and voltammetric data show that thallium(I) ions, which are adsorbed in the region of the positive surface charge, most probably, in the form of the ionic pairs, are not reduced. In this potential region, thallium(I) ions are reduced directly from the solution. At more negative potentials, the previously adsorbed stable ionic pairs slowly undergo transition into the less stable form. From this form, thallium(I) ions can be reduced or desorbed into the solution. The process is best described by a model of one electron, i.e., full charge transfer.     

Accounting for the Adsorption of Anions When Interpreting the Mechanism of Electrodeposition of Metals from Complex Electrolytes: The Reaction Order by the Electrochemically Active Ion

The relationship between the current and the bulk concentration of complex ions during concurrent specific adsorption of an electrochemically active complex ion and a complexing ligand is considered. The effect of parameters that characterize adsorption of such ions and the structure of the electrical double layer on this relationship is analyzed.__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 817–822.Original Russian Text Copyright © 2005 by Rogozhnikov.     

Adsorption of sodium octylbenzene-sulfonate at the liquid/air interface

The surface tensions of aqueous solutions containing sodium octylbenzenesulfonate were measured by means of a processor tensiometer at 20°, 25°, 30° and 35°C. A test for the layer model and thickness of the adsorbed phase is proposed. By means of a linear regression the surfactant area at liquid/air interface was calculated. Finally, the molar-and surface-related thermodynamic functions were discussed.