Computer simulation of electron transfer processes across the electrode|electrolyte interface: a treatment of solvent and electrode polarizability

A polarizable molecular dynamics model for adiabatic electron transfer across the electrode|electrolyte interface is presented. The electronic polarizability of the water and of the metal electrode is accounted for by a dynamical fluctuating charge algorithm, image charges, and the Ewald summation adapted for a conducting interface. The effects of the solvent electronic polarizability are studied by computing the diabatic and adiabatic free energy curves for both polarizable and non-polarizable water models. This represents the first effort to compute the adiabatic free energy curves from simulation for a fully polarizable electrochemical system.     

Inverse relation between polarizability and valence-electron density at the nucleus

For the hydrogen atom, the usual result for the polarizability _H is rewritten here in terms of the electron density n(0) at the nucleus as _H = . Attention is then focused on an ion in a metal, say Na⁺ in condensed metallic sodium. Using a recent result of Blazej and March for the long-range polarization interaction between the ions, the polarizability is shown to depend directly on the inverse of the valence charge displaced by the ion in its metallic environment, again evaluated at the nucleus. A brief discussion is also given, but now involving a semiclassical Thomas-Fermi approximation, for divalent ions screened by bound-state s valence electrons.     

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.     

The polarizability of a pair of hydrogen atoms at long range

The coefficients of R^?6 and R^?9 in the long-range expansion of the parallel and perpendicular components of the polarizability of a pair of hydrogen atoms at a separation R have been calculated. The results are A⁽⁶⁾₆ = 2558.59. A⁽⁶⁾_⊥ = 1268.25, A⁽⁸⁾₆ = 90639.5 and A⁽⁸⁾_⊥ = 22010.3 au. The values of A⁽⁶⁾₆ and A⁽⁶⁾₆ and A⁽⁶⁾_| are somewhat larger than previous theoretical estimates and much larger than the classical values of 729 and 182.25 au. The terms in R^?8 arise from distortion associated with the dispersion forces and from the field of the quadrupole moment induced by the field-gradient at each atom.     

Influence of the nature of the pasting liquid on the accumulation of nitroanilines at carbon paste electrode during determination by absorptive stripping voltammetry

ABSTRACT. The accumulation of ortho-, para-nitroanilines, 2,4-dimetyl-6-nitroaniline, and meta-nitrobenzoic acid at carbon paste electrode (CPE) has been studied. For the preparation of CPE different pasting liquids have been used: esters, aromatic hydrocarbons, saturated hydrocarbons, and polymethylsiloxane. Distribution ratios of o- and p-nitroanilines between the pasting liquid and water have been determined. Correlation between peak current constants and distribution ratios has been found. It has been demonstrated that during the determination of analyte on the CPE with aromatic hydrocarbons, the main influence on nitro-compound accumulation is executed by the extraction into the pasting liquids, and on the CPE with saturated hydrocarbons - by the process of depolarizer sorption onto the graphite. The selective determination of nitroanilines in the presence of hindering compounds with adsorptive stripping voltammetry has been carried out.     

On the polarizability of the sulfur atom

Using both Thole's and Birge's semiclassical models, the atomic polarizability of the sulfur atom is calculated. It is concluded that the former model is adequate for calculating polarizabilities of atoms belonging to the second row of the periodic table.     

Analytical theory of ideal polydisperse polymers at interfaces

We use a recently developed continuum theory to present an exact treatment of the interfacial properties of ideal polymers displaying Schulz-Flory polydispersity. Our results are remarkably compact and can be derived from the properties of equilibrium, ideal polymers at interfaces. We apply our theory to a number of cases, including, non-adsorbing and adsorbing surfaces, as well as telechelic chains.     

Investigation of the electrode reaction of chromium(III) at the lead dioxide electrode

Summary Using the electro-deposited lead dioxide electrode as an indicator electrode, the electrode reaction of chromium(III) was investigated in unbuffered solution covering a pH range of about 2 to 8. Reduction and oxidation peaks, the heights of which increase with chromium(III) concentration, were observed. It was found that the electrode reaction of chromium(III) at the lead dioxide electrode depends on the pH of the solution and that the reaction at a pH lower than 3 differs from that at a pH higher than 3. The lead dioxide electrode seems to be useful for the determination of chromium(III).

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Untersuchung der Elektrodenreaktion von Chrom(III) an der Bleidioxid-Elektrode

Zusammenfassung Mit der elektrolytisch belegten Bleidioxidelektrode als Indicatorelektrode wurde die Elektrodenreaktion von Chrom(III) in ungepufferter Lösung im pH-Bereich 2 bis 8 untersucht. Reduktions- und Oxidationspeaks, deren Höhe mit der Chrom(III)- Konzentration zunahm, wurden beobachtet. Es ergab sich, daß die Elektrodenreaktion vom pH der Lösung abhängt und im pH-Bereich unter und über 3 unterschiedlich ist. Die Bleidioxidelektrode scheint für die Bestimmung von Chrom(III) geeignet zu sein.

     

Linear sweep voltammetry at the tubular electrode

The theory of linear sweep voltammetry at the tubular electrode has been developed for reversible electrode processes. The convective diffusion differential equations have been transformed to an integral equation which is solved numerically. The theoretical current—potential curves at different velocities of the solution have been calculated. Comparison with experiments using a tubular electrode shows satisfactory agreement.     

The adsorption of acetylacetone at the mercury electrode

Adsorption of acetylacetone at the mercury electrode was studied in a wide pH range. Adsorption from acidic solutions is much stronger than the adsorption from basic solutions. The dependence of the differential capacity of the mercury electrode on the pH resembles the titration curve of acetylacetone. From such curves the pK of acetylacetone was calculated.     

On the electric polarizability of purple membrane

The permanent dipole moment and electric polarizability of purple membrane have been found using electrooptic methods. Comparison of the results with those for other inorganic or biological disperse particles as well as the observed effects and dynamics for a large range of applied electric field strengths support the proposal of a surface origin for the electric polarizability of purple membrane.     

Study of mass transfer enhancement on liquid/liquid interface by flow instabilities using gallium liquid electrode

Abstrac  Using liquid gallium electrodes it was proved that electrodiffusion method is a convenient tool for measuring the mass transfer at liquid/liquid interface. It was shown that mass transfer coefficient at the liquid/liquid interface at high Reynolds numbers is much more important in comparison to that measured at the solid/liquid interface at identical geometrical and hydrodynamic conditions. In experiments with the flow induced by the rotation of the upper disc (working ring electrode is placed on the bottom of the immobile disc), the Sherwood number increases in turbulent regime as Sh ∼ Re^1.8 at the liquid/liquid interface, contrary to the traditional law Sh ∼ Re^0.9 at the solid/liquid interface. In laminar regime the Sherwood number at the liquid/liquid and at the solid/liquid interfaces follows the traditional dependence Sh ∼ Re^0.5. It was shown that sharp increasing of the mass transfer coefficient at the liquid/liquid interface is closely related with the appearance of the surface waves, the phenomenon is identified as a Kelvin-Helmholtz type instability. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 4, pp. 482–490. The text was submitted by the authors in English.     

Electrocarboxylation of haloacetophenones at silver electrode

Electrocarboxylation of haloacetophenones 1 has been carried out in an undivided cell equipped with silver cathode and Mg sacrificial anode in N,N-dimethylformamide. The electroreduction behavior of these haloacetophenones at the Ag electrode was investigated using cyclic voltammetry. The electrocatalytic ability of Ag facilitated C–X bond cleavage. Methyl 4-acetylbenzoate 2 was obtained as the principal product, accompanied by acetophenone 3 and methyl 2-hydroxy-2-phenylpropanoate 4. The performances of the process were found to be dependent on synthetic conditions, such as cathode material, supporting electrolyte, electric charge, current density, and temperature. Higher yields were obtained by changing from chloro to bromo to iodo derivatives, and from ortho to para to meta isomers.     

p-character and the polarizability of molecular hydrogen

The polarizability of molecular hydrogen has been calculated over a range of internuclear separations by Hartree-Fock perturbation theory, both coupled and uncoupled, using Gaussian functions as basis set. It is shown that a relatively simple function having the proper admixture of s and p character can yield polarizabilities comparable in accuracy with those obtained from highly sophisticated wave-functions.

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Zusammenfassung Die Polarisierbarkeit des Wasserstoffmoleküls wurde für einen Bereich von Kernabständen mit Hilfe der gekoppelten als auch der entkoppelten Hartree-Fock-Störungstheorie mit einer Basis von Gauss-Funktionen berechnet. Es wird gezeigt, daß eine relativ einfache Funktion mit der geeigneten Beimischung von s- und p-Charakter Polarisierbarkeiten ergibt, deren Genauigkeit solchen aus Rechnungen mit sehr komplizierten Wellenfunktionen vergleichbar ist.

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Résumé Calcul de la polarisabilité de l'hydrogène moléculaire pour un éventail de distances internucléaires par la théorie des perturbations Hartree-Fock, couplée et non couplée, dans une base de fonctions gaussiennes. Une fonction relativement simple présentant un mélange convenable de caractère s et p fournit des polarisabilités, comparables au point de vue précision avec celles obtenues à partir de fonctions d'ondes très élaborées.

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Supported by the National Science Foundation; Grant No. GP-8359.