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Nickel is a promising alternative to noble metal catalysts for hydrogen electrocatalysis in alkaline membrane fuel cells and electrolyzers. To boost its electrocatalytic activity, it is often associated with other metals, like Cu. In this work, we combine density functional theory (DFT), Monte Carlo calculations and kinetic modeling in order to shed light on the origin of the experimentally observed activity enhancement on bimetallic NiCu nanoparticles containing ca. 5% of Cu compared to pure Ni (Topics in Catalysis, 58, (2015), 1181–1192; J. Electroanal. Chem., 783, (2016), 146–151). It is shown that the bifunctional HOR mechanism, where H ad and OH ad recombine to form water, is not viable on the monometallic Ni electrode because of the strong hydrogen adsorption and the high activation energy barrier of the recombination reaction. On bimetallic NiCu surfaces, DFT calculations predict a significant weakening of H ad adsorption energy as well as a decrease of the activation barrier of the recombination reaction for ca. 50% Cu surface coverage. Monte Carlo simulations reveal that the surface of NiCu nanoparticles is enriched in Cu atoms even for a small ( c a . 5%) Cu atomic fraction in the bulk. Kinetic modeling suggests that the experimental data for NiCu nanoparticles can be well reproduced either considering fast recombination step (bifunctional mechanism) or fast (10-fold enhancement compared to pure Ni) Volmer step (Heyrovsky-Volmer mechanism).

The data on the rate constants for ferrocene/ferrocenium (Fc/Fc + ) electron transfer in ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF 4 ]) are reported for a series of -S-(CH 2 ) n -Fc adlayers (n = 8…16) on polycrystalline gold. The values and trends are compared to the previously published data for similar series in aqueous medium, as well as to the results for ‘free’ Fc at -S-(CH 2 ) n − 1 -CH 3 modified gold in the same ionic liquid. For the latter case, the trend is opposite as compared to that in the available aqueous series (attached and ‘free’ ruthenium ammine complex): the ratio of rate constants for attached and ‘free’ reactants decreases with electrode-reactant distance in the former case, and increases in the latter. The presented comparison discovers the role of reactant and product work terms, which are essential for attached reactants as well because of conformational diversity. Corresponding contributions are estimated from molecular modeling and considered in terms of reaction volume.

Cerium redox couple is widely investigated in aqueous flow batteries due to its high redox potential. While mixed supporting electrolytes of methanesulfonic acid (MSA) and sulfuric acid have been adopted to increase the solubility and reversibility of the cerium redox reaction, the influence of such mixed ligands on the electron transfer is absent. Herein, the density functional theory is applied to study the activation energy of the electron transfer, which is in agreement with the reaction kinetics measured by electrochemical impedance spectroscopy. Cerium complexes with different ratios of methanesulfonate and sulfate ligands are assumed with optimized geometries. The standard redox potentials of these cerium complexes are calculated, which follows the same trend as the open circuit potentials of the cerium electrolyte. The exchange current densities of cerium redox couples in the electrolytes with different ratios of MSA and sulfuric acid are 0.16–0.28 mA cm−2 on glassy carbon electrode, qualitatively conforming the small variation of activation energies.

The structure of bimetallic NiCu nanoparticles (NP) is investigated as a function of their composition and size by means of Lattice MonteCarlo (LMC) and molecular dynamics (MD) simulations. According to our results, copper segregation takes place at any composition of the particles. We found that this feature is not size-dependent. In contrast, nickel segregation depends on the NP size. When the size increases, Ni atoms tend to remain in the vicinity of the surface and deeper. For smaller NPs, Ni atoms are located at the surface as well. Our results also showed that most of the metal atoms segregated at the surface area were found to decorate edges and/or form islands. Our findings agree qualitatively with the experimental data found in the literature. In addition, we comment on the reactivity of these nanoparticles. Fil: Quaino, Paola Monica. Universidad Nacional del Litoral. Instituto de Química Aplicada del Litoral. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Química Aplicada del Litoral.; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Belletti, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Instituto de Química Aplicada del Litoral. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Química Aplicada del Litoral.; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina Fil: Shermukhamedov, S. A.. Kazan National Research Technological University; Rusia Fil: Glukhov, D. V.. Kazan National Research Technological University; Rusia Fil: Santos, Elizabeth del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Institute of Theoretical Chemistry; Alemania. Universitat Ulm; Alemania Fil: Schmickler, Wolfgang. Universitat Ulm; Alemania. Institute of Theoretical Chemistry; Alemania Fil: Nazmutdinov, Renat. Kazan National Research Technological University; Rusia

Effects of adding varied amounts of copper to carbon-supported nickel particles on their structure, composition and electrocatalytic activity for the hydrogen oxidation and evolution reactions in alkaline medium have been explored. Ni1-x Cu x /C catalysts were prepared by the incipient wetness impregnation. Comprehensive characterization of the catalysts included X-ray powder diffraction, X-ray photoelectron spectroscopic, transmission electron microscopic and cyclic voltammetric analyses, while atomistic Monte Carlo simulations have been undertaken to obtain further insights into the structure of the bimetallic NiCu nanoparticles. We found that compared to monometallic Ni, NiCu nanoparticles show lower propensity towards oxidation under ambient conditions. Furthermore, we report that adding Cu allows increasing the surface-weighted electrocatalytic activity, and the specific surface area of Ni1-x Cu x /C electrodes, both contributing to a ca four-fold enhancement of the mass-weighted activity. The nature of the synergistic interactions between Ni and Cu is proposed on the basis of the analysis of experimental data and Monte Carlo structural modelling results.

A kinetic model is developed to describe the heating and evaporation of a spherical nanoparticle under the influence of a scanning tunneling microscope (STM). Simulations were performed for silicon nanoparticles of different sizes and for different STM parameters. Different kinetic features of evaporation are predicted and discussed. The lifetime of the nanoparticles is estimated and compared with original experimental data obtained for layers of silicon nanoparticles formed upon magnetron sputtering and deposited on a highly oriented pyrolytic graphite surface (HOPG).

Adsorption of a H2O molecule on Bi, Ga and Hg electrode surfaces is studied in the framework of cluster model at the density functional theory (DFT) level. At bismuth(111) single crystal plane the hollow site is energetically more preferable for the H2O adsorption (− 31.1 kJ mol− 1), while the adsorption at top site of Hg and Ga metal surfaces is confirmed to be energetically the most preferable (− 35.6 and − 24.7 kJ mol− 1, respectively). The calculations for Bi(111), Hg, and Ga are further extended to include the effect of external electrical field, and data analysis is completed with the help of the mean field approximation in order to model adsorbed water behaviour in the H2O molecules' bilayer. An associate of 13 H2O molecules is modelled in order to address the influence of lateral interactions in a water bilayer. The Ga surface is argued to be more hydrophilic than the Bi(111) and Hg surfaces. Despite the weaker adsorption energy of a single H2O molecule at the Ga surface, water molecules at the Ga/water interface are additionally stabilized by stronger hydrogen bonds. We stress the important role of the H2O bilayer at a metal electrode surface, which depends on the atomic corrugation of a metal surface.

We investigate oxygen reduction in alkaline solution with the focus on gold and silver electrodes. On the basis of theoretical considerations we propose a detailed mechanism, which we support by explicit calculations. In accordance with previous suggestions we conclude that the first step is an outer-sphere electron transfer to the oxygen molecule. The breaking of he oxygen-oxygen bond involves adsorption of OH on the electrode surface. This is much stronger on Au(100) than on Au(111), which explains why the former is a better catalyst. Fil: Ignaczak, Anna. University of Lodz; Polonia Fil: Nazmutdinov, Renat. Kazan National Research Technological University; Rusia Fil: Goduljan, Aleksej. Universitat Ulm; Alemania Fil: Moreira de Campos Pinto, Leandro. Universidade Federal do Mato Grosso do Sul; Brasil. Universitat Ulm; Alemania Fil: Juarez, Maria Fernanda. Universitat Ulm; Alemania Fil: Quaino, Paola Monica. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina Fil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Schmickler, Wolfgang. Universitat Ulm; Alemania

Density functional theory (DFT) and molecular dynamics (MD) techniques are used to study proton transfer from an aqueous solution to an Ag(1 1 1) surface. DFT is applied to study Ag–water and Ag–hydronium interactions as well as proton transfer for small systems based on the cluster model. The data gained are then used to adjust an empirical Ag–water interaction potential and to reparametrize an empirical valence-bond (EVB) model, which has been successfully applied for the study of proton transfer to a Pt(1 1 1) surface before. Employing these force fields in MD simulations enables dynamic modeling of the electrolyte–metal interface on a scale large enough to give realistic results. Results from a MD trajectory study on Ag(1 1 1) are reported and compared to the analogous study for platinum. Low discharge rates on Ag(1 1 1) are observed, and the potential range for hydrogen evolution can be estimated. The different behavior relative to Pt(1 1 1) can be traced to features of the respective potential energy surfaces and to the different structural properties of the aqueous/metallic interfaces.

Mechanism of copper underpotential deposition at stepped faces of platinum single crystals Pt(hkl) is studied using cyclic voltammetry, scanning probe microscopy, and quantum-chemical modelling. It is shown that the first stage of UPD is one-dimensional decoration of the (100)- or (110)-orientated steps, then copper monolayer forms at (111)-terraces. The final stage is the secondary step decoration. Quantum-chemical modelling, with the using of long-distance potentials of the Cu-Pt and Cu-Cu pair interactions, allows estimating the energy of copper adsorption at different structure elements of the substrate (steps, kinks, terraces) and revealing the succession of the adatom monolayer formation; it also provides additional information for the identifying of the nature of voltametric peaks for different stages of the copper adsorption-desorption.

The hydrogen absorption into overlayers of Pd deposited on Au(111) has been investigated by density functional theory (DFT). Hydrogen concentrations, absorption environments, and geometrical and electronic effects have been analyzed, seeking for a better understanding of the general principles governing the process and the effect of foreign supports. The results show that the absorption is more favored than in pure Pd leading to lower absorption energies and less repulsive interactions due to the surface expansion induced by the gold larger lattice constant. Our findings also suggest that the hydrogen absorption process is more favorable for a less number of Pd overlayers. This situation changes gradually until the substrate influence is no longer detected and the pure palladium nature appears. An entangled combination of repulsive forces, strain effect, structural ordering and chemical affinity has been found. The kinetics of hydrogen absorption has been studied as well. Two cases were explored: (1) the absorption of an adsorbed hydrogen atom and (2) the bond-breaking and penetration of a H2 molecule. Fil: Quaino, Paola Monica. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina Fil: Nazmutdinov, Renat. Kazan National Research Technological University; Rusia Fil: Peiretti, Leonardo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina Fil: Santos, Elizabeth del Carmen. Ulm University; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina

Reduction of a heteropolyanion (HPA) of the Anderson type ([CoMo6O24H6]3−) at a mercury electrode has been studied at different temperatures by using the polarographic technique. The results have been interpreted in terms of self-inhibition phenomena, which disclose non-monotonous dependence on the electrode charge. The adsorption interaction of the oxidized and reduced forms of HPA with the electrode surface was described in the framework of cluster model. The quantum chemical calculations were performed at the Density Functional Theory level. The distance-dependent electronic transmission coefficients were computed for three different orientations of [CoMo6O24H6]3− relative to the mercury surface. The planar orientation was found to be the least preferable from the viewpoint of both the adsorption energy and the orbital overlap. The experimental results have been explained qualitatively assuming the interplay between two orientations of the reduced form of HPA. The lateral interactions within the adlayer of anions (co-adsorbed with cations) were shown to be attractive and play an important role in self-inhibition.

The adsorption of the chloride ion and chlorine atom on clusters simulating the surface of the (111) and (001) faces of the crystal lattice of indium and liquid gallium are calculated using the Hartree–Fock–Roothaan and density functional (B3LYP) quantum-chemical methods. The energy of adsorption of chloride ions from a gas phase at these faces increases in the following series: bridge≈hollow < on-top positions and equals to ∼179 kJ mol–1 for In(111) and ∼183 kJ mol–1 for gallium in the on-top position. Both metals exhibit similarity in the formation of bonds between their surface atoms and the adsorbate. The adsorbate charge does not depend on the adsorbed form (chloride ion or chlorine atom) and equals ∼ 0.5e. Parameter of a virial adsorption isotherm is estimated with allowance for coulombic interactions near the metal/electrolyte interface.

The effect of the ligand surrounding on the character and degree of the inner-sphere reorganization during electroreduction of aqua, aquahydroxy, hydroxy, and Edta complexes of zinc(II) is studied in the framework of a quantum-chemical approach. It is established that the most substantial intramolecular reorganization occurs during the transfer of the first electron onto [Zn(Edta)]2–. The solvent's reorganization energy is estimated.

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.

An approach is suggested in order to investigate the mechanism of interfacial electron-transfer processes with reagents of nonspherical form and complicated charge distribution. Chelate chromium(III) ethylenediaminetetraacetate (EDTA) complexes are regarded as a good model system. A series of SCF quantum chemical calculations at the ZINDO/1 level were performed for the systems Cr(EDTA)(H2O)n- (n = 0, 1, 2, 3, and 4). A quinquedentate complex Cr(EDTA)H2O- was found to be energetically more favorable compared to Cr(EDTA)-. The interaction of Cr(EDTA)- with a cadmium electrode (modeled as a 19-atomic planar cluster) was investigated as well. The analysis of both the potential energy surfaces and the partial charge transfer allows the explanation of the absence of “specific” interaction between Cr(EDTA)- complexes and mercury-like metals observed experimentally. A way to estimate the inner-sphere contribution (Ein) to reorganization energy is proposed. The inner-sphere asymmetry (nonequality of Ein values for...

We have investigated several ways of introducing a solvated proton into a DFT calculation in order to mimic an electrochemical interface: an extra hydrogen introduced into a metal bilayer, a Zundel and an Eigen ion. In all these cases the charge on the supposed proton is substantially less than a unit positive charge. In contrast, when the electrode is represented as a cluster, the charge on Zundel ion is indeed plus one. However, the distribution of the compensating charge on the cluster is quite different from that on a plane metal surface. Fil: Quaino, Paola Monica. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Luque, Noelia Beatriz. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Soldano, Germán. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Nazmutdinov, R.. Kazan National Research Technological University; Rusia Fil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina Fil: Roman, T.. Universitat Ulm; Alemania Fil: Lundin, E.. Chalmers University Of Technology; Suecia Fil: Groß, A.. Universitat Ulm; Alemania Fil: Schmickler, Wolfgang. Universitat Ulm; Alemania

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 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.

Experimental in situ Raman spectra are presented for potassium, sodium and mixed fluoroaluminate melts. More acidic melts with cryolite ratio (CR) below 2 are accented. The cation-dependent ratio of integral band intensities is assigned to specific interactions of potassium cations with low coordinated fluoroaluminates. For alumina containing melts, the effect of potassium on the stoichiometry of predominating oxofluoroaluminate anion is observed indirectly. Density functional theory is employed to investigate the behavior of different fluoroaluminates (including dimers) and their associates formed by alkali metal cations.

The metal capacity C Me for the Pt(100)/H 2 O interface has been calculated in terms of a cluster model as a function of the electrode charge using results of MD simulations. The function C Me was found to be negative and to decrease with positive surface charges. It has been shown that the total capacity of the compact layer increases with the anodic polarization.

The structure of sodium cryolite melts was studied using Raman spectroscopy and quantum chemical calculations performed at the density functional theory level. The existence of bridged forms in the melts was argued first from the analysis of experimental Raman spectra. In the quantum chemical modelling emphasis was put on the construction of potential energy surfaces describing the formation/dissociation of certain complex species. Effects of the ionic environment were found to play a crucial role in the energetics of model processes. The structure of the simplest possible polymeric forms involving two Al centres linked through F atoms (“dimers”) was thoroughly investigated. The calculated equilibrium constants and model Raman spectra yield additional evidence in favour of the dimers. This agrees with a self-consistent analysis of a series of Raman spectra for a wide range of the melt composition.

Sputtering from plasma-facing surfaces upon particle impact can limit the lifetime of components in fusion devices, especially in the diverter region. Atomistic simulations of the processes associated with plasma–wall interactions allow for a detailed analysis of sputtering, reflection and adsorption. Most former works of beryllium sputtering by hydrogen isotopes were aimed mostly on the sputtering yield. We investigate the influence of impact energy and angle on sputtering, and analyze these quantities also for the outgoing particle. We model the sputtering by non-cumulative molecular dynamics simulations with a large number of trajectories for the various parameters. The underlying forces and energies are obtained from high-dimensional neural networks fitted to density functional calculations. We find a good agreement with the previously reported sputtering yields for perpendicular impact and a qualitative accordance with experimental data. In detail, the sputtering yield increases with increasing impact energy for angles of incidence larger than 45° with respect to the surface normal, while smaller angles show a maximal yield up to 100 eV. In cases where D reflection rather than sputtering occurs, a similar pattern is found for all angles, with the maximal reflection rate at 80°.