Renat R. Nazmutdinov

Why is Gold such a Good Catalyst for Oxygen Reduction in Alkaline Media

The two faces of gold: the reduction of oxygen on gold electrodes in alkaline solutions has been investigated theoretically. The most favorable reaction leads directly to adsorbed O(2)(-), but the activation energy for a two-step pathway, in which the first step is an outer-sphere electron transfer to give solvated O(2)(-), is only slightly higher. d-band catalysis, which dominates oxygen reduction in acid media, plays no role. The reason why the reaction is slow in acid media is also explained.

Quinones Electrochemistry in Room-Temperature Ionic Liquids

The two-step electrochemical reduction of tetrachloro-1,2-benzoquinone (chloranil), 2-methyl-1,2-benzoquinone (toluquinone), and 9,10-anthraquinone in two room-temperature ionic liquids is addressed by means of voltammetry on a platinum electrode. For the subsequent quinone/radical anion (Q/Q(•-)) and radical anion/dianion (Q(•-)/Q(2-)) redox reactions, the experimental data on formal potentials in 1-butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF(4)]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim][PF(6)]) and literature data for the same reactants in various aprotic molecular solvents are considered in the framework of a common potential sequence (Fc(+)/Fc scale) and compared with solvation energies computed at various levels. For the Q/Q(•-) couple, the agreement appeared to be satisfactory when solvation is described at the polarized continuum model (PCM) level. In contrast, for the Q(•-)/Q(2-) couple, the account for specific solvation at the molecular level is crucial.

Quantum chemical modelling of the heterogeneous electron transfer: from qualitative analysis to a polarization curve ☆

State-of-the-art in the field of quantum chemical modelling of the heterogeneous electron transfer processes is reviewed. Novel approaches originating from interplay between quantum chemistry and modern theory of charge transfer are discussed and illustrated by recent results on the calculation of relevant kinetic parameters for various electrochemical systems. Emphasis is made on the modelling of the inner-sphere reorganization and the works of approach, as well as on the consideration of reaction layer as an orientational ensemble of reagents. Recent approaches to the estimation of electronic transmission coefficient are analyzed. A possibility to employ traditional phenomenological theory to the analysis of experimental data is re-examined in the framework of microscopic treatment.

Molecular dynamics simulation studies of the mercury-water interface

Abstract Molecular dynamics (MD) simulation studies of the mercury-water interface are presented. A slab of water molecules, about 25Awide, confined by mercury phases, is investigated. A rigid water model and a flexible water model are used to describe the water-water interactions. Recently, we parameterized ab initio calculations on mercury-water clusters to describe the mercury-water potential. The liquid mercury phase is approximated as a rhombohedral lattice. The mercury-mercury interaction is modelled by a harmonic potential. Our results show a significant influence of the mercury phase on the structural and dynamic properties of the water phase. The structure of the interface is analysed in terms of density functions, radial distribution functions, orientation of the water molecules, potential drop, and hydrogen bonding characteristics.

The role of charge distribution in the reactant and product in double layer effects for simple heterogeneous redox reactions

Abstract The role of charge distribution in transition metal complexes is considered for simple heterogeneous electron transfer reactions. On the basis of quantum chemical calculations for the couples [Co(NH 3 ) 6 ] 3+/2+ , [Fe(H 2 O) 6 ] 3+/2+ , and Fe(CN) 6 3−/4− , and a simple model for the double layer, it is shown that the double layer effect for these reactions depends more on the charge on the ligands than on that on the central metal ion. The results of calculations based on the double layer model are discussed with respect to experimental data obtained at mercury and single crystal gold electrodes.

Contemporary understanding of the peroxodisulfate reduction at a mercury electrode

Specific aspects of the kinetics of anion electroreduction at high overvoltages are addressed by various traditional procedures to treat experimental data. The expansion of the Frumkin correction concept is proposed in terms of the reaction volume which increases with increasing negative electrode charge for anionic reactants. A molecular level approach based on quantum chemical calculations of the work terms and the electrode–reactant electronic coupling is employed for calculations of the reaction volume for the case of peroxodisulfate S2O82− and the ion pair Na+·S2O82−, the species which are to be considered as possible reactants in Na2S2O8 solutions with sodium salts as supporting electrolytes. Estimates of the partial rate constants for the anion and ion pair are reported as well. New experimental data are presented for solutions of equal ionic strength and equal degree of association but with different total reactant concentration. These data confirm the possibility of local ion pair formation at low negative charge. In parallel the previously ignored problem of correction for mass transport limitations is discussed for a system with two simultaneously discharging species of various charges. It follows from this reconsideration that previous data cannot be interpreted for sure as the absence of an ion pair contribution to the total current. The problem of separation of contributions from corresponding parallel steps to the total current is discussed, and the fast formation of an ion pair preceding the electron transfer was found to be rather probable.

Asymmetry of inner-sphere reorganization energy for heterogeneous electron transfer

The approach to the calculation of the activation energy of electrochemical charge transfer is considered for systems characterized by asymmetry of inner-sphere reorganization (i.e. by the difference in inner-sphere reorganization energies for direct and reverse reactions). Model calculations are carried out and the region of parameters is evaluated for which the effect is pronounced. A quantum-chemical analysis of inner-sphere reorganization is presented for four cobalt and chromium chelate aminocarboxylate complexes and the corresponding contribution to activation energy is discussed in connection with the difference in rate constants.

Monte Carlo simulation of electrochemical electron transfer processes

A Monte Carlo simulation of electrochemical electron transfer (ET) is performed at small overpotentials with the use of the Dogonadze, Kuznetsov and Vorotyntsev model (J. Electroanal. Chem. 25 (1970) App. 17). The ET process is considered as a random walk in a set of Gibbs energy surfaces (GES) corresponding to various electronic states. The method allows one to calculate the transition probability at arbitrary electronic coupling of the redox couple with the metal electrode, i.e. it covers the whole range between non-adiabatic and adiabatic limits.

Contemporary quantum chemical modelling of electrified interfaces

Attempts of describing metal/solution interfaces on the basis of cluster model and quantum chemical methods of different levels, made during the past decade, are surveyed and critically discussed. Even relatively small clusters modelling of a metal surface are shown to be an effective implement to handle fundamental problems of the double layer theory. Liophilicity of metals, dissociative water chemisorption, adsorption of hydrated ions and the contribution of a metal electrode to the interfacial capacity are topics of primary attention in this paper. In order to elaborate a new molecular model for a charged electrode surface, we consider in detail specific problems of the quantum chemical approaches and possible ways to surmount these. To supplement the picture of the state-of-the-art in the area of microscopical modelling under consideration, we report some original results concerning the study of hydrophilicity of low-index silver faces. The interplay between traditional electrochemical model concepts and “quantum chemical” language is illustrated by a great deal of both ab initio and semi-empirical calculations.

Submolecular Electronic Mapping of Single Cysteine Molecules by in Situ Scanning Tunneling Imaging

We have used L-cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and chronocoulometry, and density functional theory (DFT) computations. Cys molecules were assembled on single-crystal Au(110) surfaces to form a highly ordered monolayer with a periodic lattice structure of c(2x2) in which each unit contains two molecules; this conclusion is confirmed by the results of calculations based on a slab model for the metal surface. The ordered monolayer offers a platform for submolecular scale electronic mapping that is an issue of fundamental interest but remains a challenge in STM imaging science and surface chemistry. Single Cys molecules were mapped as three electronic subunits contributed mainly from three chemical moieties: thiol (-SH), carboxylic (-COOH), and amine (-NH2) groups. The contrasts of the three subunits depend on the environment (e.g., pH), which affects the electronic structure of adsorbed species. From the DFT computations focused on single molecules, rational analysis of the electronic structures is achieved to delineate the main factors that determine electronic contrasts in the STM images. These factors include the molecular orientation, the chemical nature of the elements or groups in the molecule, and the interaction of the elements with the substrate and tip. The computational images recast as constant-current-height profiles show that the most favorable molecular orientation is the adsorption of cysteine as a radical in zwitterionic form located on the bridge between the Au(110) atomic rows and with the amine and carboxyl group toward the solution bulk. The correlation between physical location and electronic contrast of the adsorbed molecules was also revealed by the computational data. The present study shows that cysteine packing in the adlayer on Au(110) from the liquid environment is in contrast to that from the ultrahigh-vacuum environment, suggesting solvent plays a role during molecular assembly.