Evaluation of equilibrium parameters characterizing metal oxide/electrolyte solution interface

According to the surface complexation model (SCM), charging of a metal oxide surface in aqueous environment is due to interactions of active surface groups with ions from the bulk of the solution. Several models for mechanism of surface reactions were proposed. Interfacial equilibrium is determined by corresponding equilibrium constants, but also with the structure of the electrical interfacial layer (EIL). Therefore, evaluation of equilibrium parameters is not a simple task. Traditionally, the measurements of pH dependency of surface charge density was used for that purpose. This article shows that introduction of electrokinetic data produces more reliable results, especially in the case of specific adsorption. If surface charge density and/or adsorption data are not available, one may still deduce interfacial equilibrium constants from electrokinetic results combined with measurements of the surface potential.     

The glass/electrolyte solution interface

A hydrated layer is formed on most glass/electrolyte solution interfaces. Arguments for the existence of such a layer are discussed, and concentration profiles of some ions are presented. In some cases (SiO₂ glass after short contact with water at room temperature; vitreous CaSiO₃) a hydrated layer does not exist. These results are applied to the concepts of the origin of glass electrode potentials.     

Polarization of water in the metal/electrolyte interface

This paper treats the diffuse part of the double layer by including the local polarization as a thermodynamic variable. We derive a non-local Gouy-Chapman equation which contains as physical parameters the polarization correlation length and the polarization of the first layer of water and which has the effect of dielectric saturation of the solvent built in. We obtain numerical values for the correlation length and the dielectric constant in the vicinity of the metal surface.     

Adsorption of procaine at the mercury/electrolyte solution interface

The adsorption of the local anaesthetic procaine hydrochloride at the mercury/electrolyte interface solution is followed using capacitance measurements. The adsorption is studied at various procaine concentrations, in potassium chloride, potassium bromide or potassium fluoride used as supporting electrolytes, and at various pH values and temperatures. Procaine has basic properties with two acidity constants K. The results indicate the way the procaine molecules orientate at the interface. In all cases studied no hemimicelles or condensed film are observed.     

Lyotropic effects at the silver iodide/electrolyte solution interface

The lyotropic effect in the flocculation of a negatively charged AgI sol is explained on the basis of a double layer model without specific adsorption of cations. The constant potential model for the double layer interaction gives better results than the constant charge model. The theoretical results indicate furthermore that repeptization of the flocculated sol is possible.     

On the adsorption of cetyldimethylbenzylammonium chloride at the mercury/electrolyte solution interface

The adsorption of cetyldimethylbenzylammonium chloride (CDBACl) on the hanging mercury electrode is studied in various supporting electrolytes at various temperatures from 1 to 50 degrees C. A condensed film with low capacitance is formed at negative potentials at transition temperatures below approximately 40 degrees C. The decrease of the temperature favors the film formation, and increases the width of the capacitance pit, while its value remains practically constant. Hysteresis phenomena are also observed during different scan directions. Capacitance-time curves at the potentials where the film is formed show in some cases a nucleation and growth mechanism with induction time and studied by the Avrami formulation. At high temperatures an increase of the capacitance with time is observed depending on the CDBACl concentration and slightly on the electrolyte used, and is attributed to the formation of hemimicelles. At high negative potentials a second narrow region with lower capacitance values is observed. This is easily observed at very high temperatures, while it is absent at lower temperatures. It depends upon the concentration of CDBACl and the electrolyte used. The results are different from those obtained for the adsorption of cetyltrimethylammonium bromide on mercury, indicating the importance of interaction between the hydrophobic chains.     

Electrochemical impedance simulation of a metal oxide heterostructure/electrolyte interface: A review

The results of an analysis of the literature data obtained when investigating processes of charge transfer at interfaces of heterostructures formed by various methods, including the high-energy methods, are presented in this paper. The performed investigation of oxide layers at the titanium surface, with use made of impedance spectroscopy data made it possible to reveal the nature and influence of some processes and factors on the charge transfer mechanism realized at a metal oxide heterostructure/electrolyte interface. Simulating an oxide/electrolyte interface gives one a chance to identify, in a spectrum, the responses that characterize the behavior of porous and poreless layers, as well as the responses that are due to the space-charge region formed in the oxide material and to the corrosion and diffusion processes.     

Water density in the electric double layer at the insulator/electrolyte solution interface

I studied the spatial structure of the thick transition region between n-hexane and a colloidal solution of 7-nm silica particles by X-ray reflectivity and grazing incidence small-angle scattering. The interfacial structure is discussed in terms of a semiquantitative interface model wherein the potential gradient at the n-hexane/sol interface reflects the difference in the potentials of "image forces" between the cationic Na(+) and anions (nanoparticles) and the specific adsorption of surface charge at the interface between the adsorbed layer and the solution, as well as at the interface between the adsorbed layer and n-hexane. The X-ray scattering data revealed that the average density of water in the field approximately 10(9)-10(10) V/m of the electrical double layer at the hexane/silica sol interface is the same as, or only few percent higher (1-7%) than, its density under normal conditions.     

Quasi-reversible faradaic depolarization processes in the electrokinetics of the metal/solution interface

Bipolar faradaic depolarization of the metal/solution interface is quantitatively analyzed for the case where the solution is subject to lateral flow and contains a quasi-reversible redox couple. Transversal convective diffusion of the electroactive species and a position-dependent degree of reversibility of the interfacial electron-transfer (e.t.) reaction are among the primary features that govern depolarization. The spatial distributions of species concentrations and electric potential are numerically simulated. The system is characterized by nonlinear coupling between the transport (diffusion and flow) and the electric potential distribution under conditions of finite local currents. The resulting picture is that the reversibility of the e.t. reaction varies with position on the surface, with the highest reversibility downstream. This, in itself, generally leads to strongly asymmetric profiles of the faradaic current density along the surface. The impact on the electrokinetic properties of the interface is huge. For example, the steady-state streaming potential is depressed by the contribution from the bipolar faradaic process to the back current to an extent that varies from insignificant to complete, depending on the e.t. rate constant and concentrations of the electroactive species.     

Revealing the solid electrolyte interface on calcium metal anodes

Owing to its low potential, crustal abundances and environmental friendliness, calcium metal anode(CMA) is emerging as a powerful contender in post-lithium era. However, the passivation of CMA fatally hinders its development. Recently, several feasible electrolytes have been developed. Nevertheless, as a pivotal part, the solid electrolyte interface(SEI) formed on CMA has not been paid enough attention to. In this review, based on the passivation mechanism of CMA, the favorable composition of SE...     

Kinetic Monte Carlo study of proton binding at the metal oxide/electrolyte interface

The kinetics of proton binding at the metal oxide/electrolyte interface is studied using the kinetic Monte Carlo method. The influence of system properties (surface site density, interfacial dielectric constant, surface energetic heterogeneity) on the equilibrium and kinetic surface coverage is shown. It is shown that the kinetic properties are much more sensitive to lateral interactions than the equilibrium ones. The assumption of energetic heterogeneity rapidly changes the time scales of the processes as well as the time interval between two subsequent elementary processes. In this paper, the atomistic insight into the kinetics of H(+) ion uptake at the metal oxide/electrolyte interface is presented for the first time.     

Influence of inhibitor structure and metal/solution interface on the corrosion resistance of the protected metal

Seven systems of more than 60 compounds with possible inhibiting properties are investigated. Several methods are used: electrochemical, gravimetric, XPS, and SEM analyses. The inhibition efficiency Z is related to the chemical structure of inhibitors (sequences of compounds with regard to Z are found), their electronic structure, the surface area of the inhibiting molecule, and the structure and composition of the metal/solution interface (impedance, adsorption equilibrium parameters, etc.). The most efficient of the investigated inhibitors have Z = 94–99%. Conclusions are drawn which allow identification of compounds with prognosticated inhibiting action. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 11, pp. 1352–1364. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Thermodynamics of the N2/N3- redox couple in a LiBr-KBr-CsBr melt

Nitrogen electrode reaction has been investigated in a LiBr-KBr-CsBr melt containing Li3N. The reaction N3- --> 1/2N2 + 3e- is confirmed by quantitative analysis of anodically evolved gas. The Nernst relation holds for the rest potential of Ni electrodes at a nitrogen gas pressure, pN2, of 0.05-1.0 atm and an anion fraction of the N3- ions, xN3-, of 0.003-0.010 (anion fraction). Then, the standard formal potential of the N2/N3- couple, , is evaluated to be 0.251 +/- 0.009 V versus Li+/Li (pN2 = 1 atm, xN3- = 1) at 673 K. The dependence of on the temperature (570-730 K) gives a linear relation, whose slope is (-0.930 +/- 0.117) x 10(-3) V K(-1). Thermodynamic quantities for the formation of Li3N in the melt are also estimated.     

The standard redox potential of the phenyl radical/anion couple

The voltammogram of aryldiazonium tetrafluoroborates in acetonitrile (ACN), at low concentration, shows a first one-electron wave followed at a more negative potential by a small second wave; this last one corresponds to the reduction of the radical formed at the level of the first wave. Simulation of the voltammogram permits one to determine the standard redox potential of the radical/anion couple Eo(Ph./Ph-) = 0.05 V/SCE and the reduction mechanism of the diazonium cation. An electron transfer concerted with the cleavage of the C-N bond furnishes the aryl radical; this radical undergoes two competitive reactions: reduction at the electrode and H-atom transfer.     

A new radiotracer method of adsorption studies at metal oxide/aqueous electrolyte interface

Adsorption of inorganic ions at the titania/electrolyte solution interfaces has been studies using a radioisotopic technique. Adsorption evaluated from uptake of radioactivity from the solution is compared with that obtained from sediment radioactivity.     

The influence of temperature on the measurement of the impedance at the AgI/electrolyte solution interface

Results of capacitance measurements are presented for solutions of 0.0005 M to 1 M KNO₃ at 25 and 80°C, and for 0.0005 M to 1 M Li?, K?, Rb? and CsNO₃ at 80°C.An alternative way to determine the capacitance per unit surface area is proposed, based on the concentration dependence of the capacitance in the Gouy-Chapman-Stern picture of the double layer.The infuence of the temperature on the measurement of the impedance at the AgI/electrolyte solution interaace is discussed, based on an equivalent circuit of the AgI-film consisting of a network of passive elements.     

Influence of the electrolyte cation and anion sizes on the redox process of PPy/PVS films in acetonitrile solution

Polypyrrole/poly(vinyl sulfonate) (PPy/PVS) films have been synthesized by a potentiodynamic method in aqueous solution. The voltammetric study of this polymer in acetonitrile (MeCN) reveals an anomalous behavior of its redox process in the three electrolytes used: LiClO₄, LiF₃CSO₃, and (Bu)₄NClO₄. The anion and cation sizes of the electrolyte clearly affect the reduction/oxidation process of a PPy/PVS film in MeCN medium. This result is explained by both anions and cations participating during the redox reaction of this polymer in MeCN medium: initially, the cations penetrate the polymer forming ion pairs with sulfonate groups, and the anions behave as the main mobile species during the potential sweeps. However, a large cation or anion will penetrate with difficulty inside the polymer, providing a lower amount of electroactive polymeric chains and a lower value of peak charges.