Adsorption on well-defined solid surfaces: Bromide adsorption on a (110) face of silver

The adsorption of bromide has been studied on a (110) face of silver by means of mixed solutions with hexafluorophosphate as base electrolyte. From the differential capacity-potential curves, the adsorbed charge of bromide was determined as functions of the electrode charge and the potential. The components of the inner-layer capacity have been determined for the two peaks always observed on the (110) face in the presence of specific adsorption. For the more negative peak potential, the component at constant amount adsorbed confirms the essential contribution of the orientation of water dipoles to the existence of this peak. On the other hand, the component at constant electrode charge indicates a non0linear electrode charge dependence of the standard Gibbs energy of adsorption. For the less negative peak potential, the two components of the inner-layer capacity seem to show that the bromide adsorption is mainly responsible for the appearance of the second peak.Different structures of the layer of adsorbed ions are proposed for different coverages of the surface. A pseudohexagonal structure, equivalent to the c (4×2) structure, corresponds to the adsorbed charge determined at saturation.     

电极/溶液界面单分子吸附层的统计力学处理 IV. 水溶液中银单晶电极的内层微分电容

根据本文系列I~[6]提出的电极/溶液界面溶剂化层偶极取向分布模型, 拟合计算Ag(111)、Ag(100)及Ag(110)/水溶液界面的内层微分电容(C_1)～表面电荷密度(σ)变化关系。表明在银电极上, 吸附水分子似分别稳定在金属原子点阵的顶位(111)或穴位(100)及(110)。讨论了溶剂化层的结构与性质对C_1～σ曲线可能产生的影响。     

电极/溶液界面单分子吸附层的统计力学处理 I. 非水溶液中汞电极的内层微分电容

本文提出电极/溶液界面溶剂化层偶极取向分布模型, 应用统计力学方法及热力学平衡条件导出普遍化的单层吸附等温方程, 其电解质溶液的溶剂组成可以是纯态的或混合物(多组份)的. 文中分别以甲酰胺、碳酸亚乙酯和甲醇等三种纯溶剂的汞/溶液界面为例, 采用曲线拟合计算内层微分电容随表面电荷变化关系。预计本模型处理对汞/水溶液或汞/(混合溶剂)溶液界面仍可适用。     

Effect of the nature of the metal on the dielectric properties of polar liquids at the interface with electrodes. A phenomenological approach

The dielectric behaviour of water, DMSO and ACN at the interface with transition and non-transition metals is examined by analysing the inner-layer capacity as a function of the metal surface chemical affinity. An, inner-layer capacity in the absence of metal-solvent specific interaction is defined and derived by graphical correlations. The permittivity of the surface phase of the solvent under these conditions is derived and analysed to elucidate the nature of the factors contributing to the dielectric behaviour at an interface. The capacity-potential curves for Fe, as a typical transition metal, are elaborated to investigate the orientation of the solvent on the surface and the applicability of the Gouy-Chapman-Stern model. Suggestions on the nature of the metal-water surface bond are given on the basis of the derived parameters. The structure of the double layer in ACN at transition metals is discussed in the light of recent measurements.     

电解液离子与炭电极双电层电容的关系

以酚醛树脂基纳米孔玻态炭(NPGC)为电极, 通过微分电容伏安曲线的测试, 研究了水相体系电解液离子与多孔炭电极双电层电容的关系. 结果表明, 稀溶液中, 多孔炭电极的微分电容曲线在零电荷点(PZC)处呈现凹点, 电容降低, 双电层电容受扩散层的影响显著；若孔径小, 离子内扩散阻力大, 电容下降更为迅速, 扩散层对双电层电容的影响增大. 而增大炭材料的孔径或电解液浓度, 可明显减弱甚至消除扩散层对电容的影响. 炭电极的单位面积微分电容高, 仅表明孔表面利用率高, 如欲获得高的电容量, 还要有大的比表面积. 离子水化对炭电极的电容产生不利影响, 选用大离子和增大炭材料的孔径, 可有效降低离子水化对炭电极电容性能的影响.     

交流示波极谱法中i~f-E曲线的研究 8:"电极/溶液"界面动态双电层微分电容的快速测量

"电极/溶液"界面动在记双电层微分电容是电极过程动力学中一个重要的物理量,但其测量方法,多数仍停留在对逐一测定的数据点进行作图分析上.本文以i~f-E曲线上电流峰的理论公式为基础,提出了一个快速测量"电极/溶液"界面动态双层微分电容的新方法.     

The dependence of the kinetics of some simple outer-sphere electrode reactions on the nature of the electrode material

The kinetics of a number of simple inorganic electrode reactions that are known or expected to follow outer-sphere pathways have been examined at mercury, silver, platinum, and gold-aqueous interfaces in order to explore the effects of varying the electrode material on outer-sphere reactivity. The electroreduction kinetics of Co(III) ammine complexes exhibited only mild dependences on the nature of the electrode material which were compatible with the expected variations in double-layer effects. However, the electrooxidation of Cr²⁺ proceeded at strikingly higher overpotentials on the solid surfaces compared with mercury electrodes. Similar effects were also seen for the electrooxidation of V²⁺, Eu²⁺ and Ru²⁺ in the presence of Cr²⁺. Much larger rate constants were observed for these aquo reactions at solid surfaces in the absence of Cr²⁺, although Cr²⁺ had no influence on Co(NH₃)₆³⁺ electroreduction, or any reaction at mercury electrodes. It is speculated that the very large substrate effects upon the electrode kinetics of aquo couples arise from the influence of the inner-layer water structure on the reactant-solvent interactions experienced by these “structure-making” reactants at their plane of closest approach. The inhibiting influence of Cr²⁺ may be due to its ability to efficiently remove adsorbed catalytic contaminants by incorporation into a substitutionally inert Cr(III) electrooxidation product by means of a ligand-bridge mechanism.     

Study of the (210) face of gold in aqueous solutions

Among all the gold faces studied to date, the (210) face has the most negative pzc and therefore should be less affected by preoxidation than the other faces. But the (210) gold face-sodium fluoride solution interface is ideally polarizable only in a short range of potential. Nevertheless, differential capacity-potential curves have been tentatively exploited. There seems to be adsorption of the fluoride ions on the (210) face of gold. The inner-layer capacity-charge curves are discussed.     

Double-layer effects in potentiometric stripping analysis

A model for prediction of the background signal (E vs. t) in potentiometric stripping analysis is presented and shown to be consistent with experimental measurements. In the absence of oxidizable material on the working electrode, it is the double-layer capacity which determines the E vs. t function. Surfactants present in solution give rise to marked interferences, because of their effect on the double-layer capacity.     

Adsorption properties of polycrystalline and single crystal electrodes and the influence of surface inhomogeneity

It is shown that the adsorption of some neutral organic compounds on individual faces of a zinc single crystal can be described by the Frumkin-Damaskin theory with the use of the two parallel capacitors model. For a polycrystalline electrode a departure from the two parallel capacitors model is observed which is due to the energetic inhomogeneity of the surface. A method is suggested for calculation of the adsorption isotherm, and of the dependence of the surface coverage θ on the potential of a polycrystalline electrode, from capacity measurements data under the condition that for all n crystallographic faces (grains) exposed on the surface, the difference (C_on ? C′_n) is the same (C_on and C′_n are the double layer capacities in the supporting electrolyte solution and at θ = 1 of the n-th face, respectively). An adsorption isotherm is proposed for a uniformly inhomogeneous surface which takes account of the attractive interaction between adsorbate particles. Some methods are suggested for evaluation of the surface inhomogeneity factor (f). This factor has been determined from adsorption data for cyclohexanol and n-amyl alcohol. The differential capacity curves measured on polycrystalline zinc in the presence of cyclohexanol are in good agreement with the calculated curve for a uniformly inhomogeneous surface.     

新型非对称电化学电容器的电极匹配研究

活性炭负极容量的有效利用率是导致双电层电化学电容器和C/Ni(OH)2非对称电化学电容器容量性质差异的主要因素,并可将其作为非对称电化学电容器容量设计和测算的依据;本文引入Ni(OH)2正极有效活性物质概念,以正极有效活性物质的量匹配负极的设计容量,从而优化正、负极的容量匹配,改善非对称电化学电容器的容量和大电流性能.     

锰酸镧双层复合电极的制备和性能的研究

固体氧化物燃料电池（ Solid Oxide Fuel Cell, SOFC）是一种很有希望的新型能源转换系统 .它具有能量转换效率高、可利用燃料范围广、低排放等普通热机所无法比拟的优点,已倍受人们的关注 .　　锶掺杂的锰酸镧（ La1－ xSrxMnO3, LSM）由于具有高的电子导电性和对氧还原的良好的电催化活性,以及它和钇稳定的氧化锆（ YSZ）都有良好的热稳定性和化学稳定性,因此是目前广泛使用的阴极材料 .以 YSZ为固体电解质的固体氧化物燃料电池的一个主要缺点是操作温度太高（约为 1273 K）,如果把电池的操作温度降低到 873－ 1073 K,则…     

Adsorption of 2,2′-bipyridine at an Au(111)|ionic liquid electrified interface

The adsorption of added 2,2′-bipyridine (2,2′-BP) from 1-ethyl-2,3-dimethyl imidazolium bis(trifluoromethanesulfonyl)imide (EMMImNTf₂) at an Au(111) electrode has been investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Addition of 2,2′-BP to the ionic liquid clearly modifies the interfacial region as a result of the competition between 2,2′-BP and EMMImNTf₂ to occupy the electrode surface. Within the region of ideal polarizability, the 2,2′-BP adlayer undergoes structural changes, shown by the presence of peaks in the CV curves. Between −0.2 V and + 0.9 V, the capacitance–potential curves obtained from EIS data present a capacity maximum depending strongly on the ac frequency, which is typical pseudo-capacitive behavior indicative of a reorganization of the interfacial layer. At more positive potentials a true capacity value close to 10 μF.cm^− 2 and invariant with the potential suggests that the 2,2′-BP molecules adopt a perpendicular orientation with the nitrogen atoms facing the electrode surface, similar to their adsorption on gold from aqueous solutions.     

Calculation of the dynamic impedance of the double layer on a planar electrode by the theory of electrokinetics

Applications of microelectromechanical systems in the biotechnological arena (bioMEMS) are a subject of great current interest. Accurate calculation of electric field distribution in these devices is essential to the understanding and design of processes such as dielectrophoresis and AC electroosmosis that drive MEMS-based devices. In this paper, we present the calculation of the electrical double-layer impedance (Z(el)) of an ideally polarizable plane electrode using the standard model of colloidal electrokinetics. The frequency variation of the electrical potential drop across the double layer above a planar electrode in a general electrolyte solution is discussed as a function of the electrode zeta potential zeta, the Debye length kappa(-1), the electrolyte composition and the bulk region thickness L.     

Dynamic diffuse double-layer model for the electrochemistry of nanometer-sized electrodes

A dynamic diffuse double-layer model is developed for describing the electrode/electrolyte interface bearing a redox reaction. It overcomes the dilemma of the traditional voltammetric theories based on the depletion layer and Frumkin's model for double-layer effects in predicating the voltammetric behavior of nanometer-sized electrodes. Starting from the Nernst-Planck equation, a dynamic interfacial concentration distribution is derived, which has a similar form to the Boltzmann distribution equation but contains the influence of current density. Incorporation of the dynamic concentration distribution into the Poisson and Butler-Volmer equations, respectively, produces a dynamic potential distribution equation containing the influence of current and a voltammetric equation containing the double-layer effects. Computation based on these two equations gives both the interfacial structure (potential and concentration profiles) and voltammetric behavior. The results show that the electrochemical interface at electrodes of nanometer scales is more like an electric-double-layer, whereas the interface at electrodes larger than 100 nm can be treated as a concentration depletion layer. The double-layer nature of the electrode/electrolyte interface of nanometer scale causes the voltammetric responses to vary with electrode size, reactant charge, the value of formal redox potential, and the dielectric properties of the compact double-layer. These voltammetric features are novel in comparison to the traditional voltammetric theory based on the transport of redox molecules in the depletion layer.     

Polarography in hexamethylphosphoramide: Effect of supporting electrolyte cations

Polarographic reductions of various metal ions such as the silver, cupric, zinc, cobaltous, nickel, ferric, ferrous ions and hydrogen ion in hexamethylphosphoramide (HMPA), have been investigated in the supporting electrolytes with various perchlorates. The reduction of most of these ions is strongly influenced by the cation of the supporting electrolyte. In the presence of the tetraethylammonium ion, when the size of the cation of the supporting electrolyte is small and easily adsorbed on the negatively charged electrode surface, the reductions of metal ions are controlled by some preceding processes and are naturally irreversible. The rate of reduction becomes more rapid with the increase of the size of the cation. Thus, in Hex₄NClO₄ or LiClO solutions, the reduction of these various metal ions takes place almost totally under diffusion control, although the waves of most of metal ions show a maximum. These effects of the cation of the supporting electrolytes on reduction can be explained as a phenomenon occurring on the electrode surface. This phenomenon has been reported in previous papers [1] on the reductions of the alkali and alkaline earth metal ions. The difference in the electrocapillary curves in these solutions is rarely shown at the potential around the electrocapillary maximum, but it is very obviously shown at more negative potential. The difference in the effect of the size of the cation of the supporting electrolyte on reduction of metal ion coincides well with the difference in the electrocapillary curves in these solutions: the effect of the size of the supporting electrolyte cation on the polarographic reduction is rarely shown at the potential around the electrocapillary maximum, but it is very obviously shown at more negative potential; therefore this effect is due to the electrode double-layer difference.     

Design of hierarchical double-layer NiCo/NiMn-layered double hydroxide nanosheet arrays on Ni foam as electrodes for supercapacitors

Reasonably designing the structure of composite materials and effectively increasing electroactive sites of electrode materials are considered as the promising approaches to enhance the electrochemical performance for supercapacitors. Herein, a double-layer layered double hydroxide nanosheet array grown on Ni foams is constructed through a facile two-step hydrothermal method. The as-prepared double-layer electrode materials including Ni, Co, and Mn elements possess large surface area and porosity; thus, it can increase the contact between electrolytes and the electrode materials, which leads to an increase in electroactive sites and high electrochemical performance. The double-layer electrode shows a high capacitance performance (2950 F/g at 1 A/g) and superior cycling stability (79% retention after 10,000 cycles at 10 A/g). In addition, the asymmetric NiCo/NiMn-LDHs//AC device is fabricated and manifests good capacity with excellent cyclic stability of 82.2% after 10,000 cycles.     

Determination of electrical double-layer parameters for the adsorption of neutral molecules at the electrode–solution interface

The study of the structure of the electrode–solution interface usually involves the measurement of the differential capacity–potential characteristics of the system. In order to obtain the double-layer parameters from these data, integration and differentiation procedures are required and, for this purpose, the use of computational methods is of great value. Two computer programs have been written for the treatment of data for the adsorption of neutral molecules on electrodes. The programs use the charge density and the electrode potential as the electrical variable, respectively, and, in both cases, the differentiation procedures have been optimized by the use of an adequate numerical function. The advantages of doing a simultaneous analysis on both electrical variables are pointed out.     

Electrochemical behaviour of iron in H2SO4 containing thiophene

The effect of thiophene on the corrosion of iron in H₂SO₄ has been studied by double-layer capacity and polarisation measurements. No change in mechanism was observed by the addition of thiophene, but a significant decrease in the rate of hydrogen evolution was observed. The inhibitor concentration was found to have a significant influence on the behaviour of the open-circuit capacitance, while the change in potential was small. The results show that thiophene is adsorbed on the iron surface according to the Temkin isotherm. The inhibitor efficiencies, as determined from current-voltage curves and the weight loss method, were consistent.