Interactions of anions and cations in carbon nanotubes

We consider the insertion of alkali-halide ion pairs into a narrow (5,5) car- bon nanotube. In all cases considered, the insertion of a dimer is only slightly exothermic. While the image charge induced on the surface of the tube favors insertion, it simultaneously weakens the Coulomb attraction between the two ions. In addition, the anion experiences a sizable Pauli repulsion. For a one dimensional chain of NaCl embedded in the tube the most favor- able position for the anion is at the center, and for the cation near the wall. The phonon spectrum of such chains shows both an acoustic and an optical branch.Fil: Mohammadzadeh, Leila. Universitat Ulm. Faculty Of Natural Sciences; Alemania. Universidad Nacional del Litoral; ArgentinaFil: Quaino, Paola Monica. Universidad Nacional del Litoral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Schmickler, Wolfgang. Universitat Ulm. Faculty Of Natural Sciences; Alemani

A model for the effect of ion pairing on an outer sphere electron transfer

Ion pairing can strongly affect the rates of electron transfer reactions. To explain this effect we propose a model Hamiltonian which describes the interactions between the pairing ion and the reactant, solvent and inner sphere reorganization, and bond breaking. Explicit expressions for the energies of the initial and final states, and for the energy of activation are derived in the weak adiabatic limit. The model is applied to the reduction of Cu(II) in the presence of chloride ions. For this purpose the pertinent system parameters are obtained from density functional theory. Our model explains, why chloride enhances the rate of the first electron transfer in copper deposition.Fil: Nazmutdinov, Renat. Kazan National Research Technological University; RusiaFil: 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.; ArgentinaFil: Colombo, Estefanía. 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.; ArgentinaFil: Santos, Elisabeth. Universitat Ulm. Faculty Of Natural Sciences. Institute Of Theoretical Physics; AlemaniaFil: Schmickler, Wolfgang. Universitat Ulm. Faculty Of Natural Sciences. Institute Of Theoretical Physics; Alemani

A first principles study of the hydrogen reaction in alkaline media: OH effect

The effect of the electrolyte on the hydrogen electrode reaction (HER) has been investigated. As a starting point, we centered our studies on the Volmer reaction in alkaline media -H 2O+e -→H ad+OH -- on a Pt(111) surface. The adsorption process of the reaction intermediate H ad was investigated by quantum chemical calculations. Our analysis focused on the interaction of the OH and the H ad with the electronic bands of the metal electrode. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.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; ArgentinaFil: Arce, Mauricio Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Santos, Elizabeth del Carmen. Universidad Nacional de Córdoba; Argentina. 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; ArgentinaFil: Schmickler, Wolfgang. Universitat Ulm; Alemani

Understanding the structure and reactivity of NiCu nanoparticles: An atomistic model

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; ArgentinaFil: 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; ArgentinaFil: Shermukhamedov, S. A.. Kazan National Research Technological University; RusiaFil: Glukhov, D. V.. Kazan National Research Technological University; RusiaFil: 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; AlemaniaFil: Schmickler, Wolfgang. Universitat Ulm; Alemania. Institute of Theoretical Chemistry; AlemaniaFil: Nazmutdinov, Renat. Kazan National Research Technological University; Rusi

Decoración de Au y Pt sobre los bordes de escalón de grafito pirolitico altamente orientado

En este trabajo se presentan los resultados del estudio de la caracterización electroquímica de las Decoraciones de Oro y Platino sobre Grafito Pirolitico Altamente Orientado (HOPG) como cátodos midiendo la actividad electrocatalítica con respecto a la reacción de desprendimiento de hidrógeno (RDH) en medio ácido. Se realizaron curvas corriente potencial (I vs V) obtenidas potenciostaticamente bajo atmósfera de nitrógeno en una solución de H2SO4. La morfología de los depósitos se evaluó ex situ mediante SEM (microscopio electrónico de barrido) Los resultados permiten evaluar que las nanoestructuras generada varían su forma debido a la topografía del HOPG y su potencial aplicación como materiales de electrodo para la generación electrolítica de hidrógeno en medio ácido.In this paper we present the results of the electrochemical characterization of gold and platinum decorations on Highly Oriented Pyrolytic Graphite (HOPG) as cathodes by measuring the electrocatalytic activity with respect to the hydrogen evolution reaction (RDH) in acid medium. Current curves were potential (I vs. V) obtained potentiostatically under nitrogen in a solution of H2SO4. The deposit morphology was assessed ex situ by SEM (scanning electron microscope) results to assess the generated nanoesctructuras vary its shape due to the topography of HOPG and their potential application as electrode materials for electrolytic hydrogen generation means acid.Fil: Fuentes, Ana Silvina. Universidad Nacional de Catamarca. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Avalle, Lucia Bernardita. Universidad Nacional de Catamarca. Facultad de Ciencias Exactas y Naturales; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Quaino, Paola Monica. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santos, Elizabeth del Carmen. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

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 O2- , but the activation energy for a two-step pathway, in which the first step is an outersphere electron transfer to give solvated O2-, 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.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; ArgentinaFil: Luque, N. B.. Institute of Theoretical Chemistry; AlemaniaFil: Nazmutdinov, Renat. Kazan National Research Technological University; RusiaFil: Santos, Elisabeth. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Schmickler, Wolfgang. Institute of Theoretical Chemistry; Alemani

Hydrogen evolution on a pseudomorphic Cu-layer on Ni(111) - a theoretical study

Hydrogen evolution on a monolayer of copper on Ni(1 1 1) has been investigated by a combination of density functional theory and a model developed in our own group. The lattice constant of nickel is only about 2.5% shorter than that of copper; therefore the nickel substrate has only a minor effect on the surface d band of the adsorbed copper. However, there is a strong chemical effect which enhances the interaction of hydrogen with the Cu/Ni(1 1 1) surface as compared to Cu(1 1 1). Consequently, the adlayer promises to be a cheap catalyst that is significantly better than pure copper.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; ArgentinaFil: Quaino, Paola Monica. Ulm University; Alemania. Universidad Nacional del Litoral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Hindelang, Peter F.. Ulm University; AlemaniaFil: Schmickler, Wolfgang. Ulm University; Alemani

Oxygen reduction reaction (orr) on bimetallic AuPt and AuPd(1 0 0)–electrodes: Effects of the heteroatomic junction on the reaction paths

The seek for materials to enhance the oxygen reduction reaction (orr) rate is a highly relevant topic due to its implication in fuel cell devices. Herein, the orr on bimetallic electrocatalysts based on Au-M (M = Pt, Pd) has been studied computationally, by performing density functional theory calculations. Bimetallic (1 0 0) electrode surfaces with two different Au:M ratios were proposed, and two possible pathways, associative and dissociative, were considered for the orr. Changes in the electronic properties of these materials with respect to the pure metals were acknowledged to gain understanding in the overall reactivity trend. The effect of the bimetallic junction on the stability of the intermediates O 2 and OOH was also evaluated by means of geometrical and energetic parameters; being the intermediates preferably adsorbed on Pt/Pd atoms, but presenting in some cases higher adsorption energies compared with bare metals. Finally, the kinetics of the O–O bond breaking in O 2 ∗ and OOH ∗ adsorbed intermediates in the bimetallic materials and the influence of the Au-M junction were studied by means of the nudge elastic-band method. A barrierless process for the scission of O 2 ∗ was found in Au-M for the higher M ratios. Surprisingly, for Au-M with lower M ratios, the barriers were much lower than for pure Au surfaces, suggesting a highly reactive surface towards the orr. The O–O scission of the OOH ∗ was found to be a barrierless process in Au–Pt systems and nearly barrierless in all Au–Pd systems, implying that the reduction ofO 2 in these systems proceeds via the full reduction of O 2 to H 2 O, avoiding H 2 O 2 formation.Fil: Schulte, Erica Daniela. 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.; ArgentinaFil: Belletti, Gustavo Daniel. 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.; ArgentinaFil: Arce, Mauricio Damián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: 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.; Argentin

Unravelling the enhanced reactivity of bulk CeO 2 doped with gallium: A periodic DFT study

Doping CeO2 with gallium leads to promising materials with application in hydrogen purification processes for fuel cells. The bulk ceria?gallia is investigated by ab initio calculations. The outstanding reactivity is explained by important relaxations induced by gallium in the ceria host, having a strong impact in the electronic structure. As a result, the mixed oxide is found to be more reducible than the pure oxides in agreement with experimental data. It is thus possible to correlate structure and reactivity of the doped system on the molecular level, representing a step forward to the rational design of materials with selected properties.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; ArgentinaFil: Syzgantseva, Olga. Université Pierre et Marie Curie; FranciaFil: Siffert, Luca. Université Pierre et Marie Curie; FranciaFil: Tielens, Frederik. Université Pierre et Marie Curie; FranciaFil: Minot, Christian. Université Pierre et Marie Curie; FranciaFil: Calatayud, Monica. Universite de Paris; Franci

Why Silver Deposition is so Fast: Solving the Enigma of Metal Deposition

A perfect match: Silver deposition is one of the fastest electrochemical reactions, even though the Ag+ ion loses more than 5 eV solvation energy in the process. This phenomenon, an example of the enigma of metal deposition, was investigated by a combination of MD simulations, DFT, and specially developed theory. At the surface, the Ag+ ion experiences a strong interaction with the sp band of silver, which catalyzes the reaction.Fil: Pinto, Leandro M. C.. Universidade Estadual Paulista Julio de Mesquita Filho. Facultad de Filosofia E Ciencias-campus de Marilia; Brasil. Universitat Ulm; AlemaniaFil: Spohr, Eckhard. Universitat Duisburg - Essen; AlemaniaFil: 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 Santa Fe; ArgentinaFil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto de Física "Enrique Gaviola"; ArgentinaFil: Schmickler, Wolfgang. Institute Of Theoretical Chemistry; Alemania. Universitat Ulm; Alemani