The electrochemical stability of thiols on gold surfaces

In this paper we present a comparative analysis of the electrochemical stability of alkanethiols, aromatic and heterocyclic thiols on the Au(111) and Au(100) faces in relation to the theoretical energetic data. The peak potential and surface coverage are used as the key parameters to estimate the electrochemical stability while work function changes, adsorption energies and surface free energies calculated from periodic DFT, including van der Waals interactions, are used for the theoretical estimation. We find that the peak potentials do not correlate with work function changes and adsorption energies in particular for aromatic and heterocyclic thiols. In contrast, the reductive desorption potentials for the different thiols show a good correlation with the surface free energy of the SAMs estimated by density functional theory calculations. Surface coverage is a key factor that controls reductive desorption through van der Waals interactions.Fil: Salvarezza, Roberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Carro, Pilar. Universidad de La Laguna; Españ

Validity of the linear growth equation for interface evolution for copper electrodeposition in the presence of organic additives

The interface evolution of copper electrodeposits produced on copper from a thiorea-derivative-containing acid plating bath at a low current density and 298 K was studied by atomic force microscopy (AFM). The dynamic scaling theory was applied to AFM images leading to scaling exponents, which are consistent with the predictions of the complete linear equation for interface growth. In agreement with the theory, experimental data show, for the interface evolution, a crossover from a surface diffusion controlled regime to an Edwards-Wilkinson regime as the length scale increases.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

The electrochemical stability of thiols on gold surfaces

In this paper we present a comparative analysis of the electrochemical stability of alkanethiols, aromatic and heterocyclic thiols on the Au(111) and Au(100) faces in relation to the theoretical energetic data. The peak potential and surface coverage are used as the key parameters to estimate the electrochemical stability while work function changes, adsorption energies and surface free energies calculated from periodic DFT, including van der Waals interactions, are used for the theoretical estimation. We find that the peak potentials do not correlate with work function changes and adsorption energies in particular for aromatic and heterocyclic thiols. In contrast, the reductive desorption potentials for the different thiols show a good correlation with the surface free energy of the SAMs estimated by density functional theory calculations. Surface coverage is a key factor that controls reductive desorption through van der Waals interactions.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The role of a slow phase formation process in the growth of anodic silver oxide layers in alkaline solutions—I. Electroformation of Ag(I) oxide layer

The anodic electroformation of silver (I) oxide layer on polycrystalline silver electrodes in 0.1 M NaOH was studied by using potentiodynamic and potentiostatic techniques. The growth of the silver oxide layer under a linear potential sweep or potential step measurements involves as a first step the electroformation of Ag2O or AgOH monolayer at potentials close to the Ag/Ag2O reversible electrode potential. This monolayer grows through a solid diffusion mechanism to form a 3-D primary silver (I) oxide. Subsequently the building up of a secondary silver (I) oxide layer is clearly noticed when the potential exceeds 0.24 V (vs sce). The formation of this layer can be described in terms of an instantaneous nucleation and 3-D growth mechanism under diffusion control. The ageing effects at the primary layer level decreases the nucleation rate so that for the growth of the secondary layer an intermediate situation between instantaneous and progressive nucleation under diffusion control can be observed. The secondary silver (I) oxide layer can be related to the aged silver (I) oxide species previously reported.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

The electrodissolution and passivation of mild steel in alkaline sulphide solutions

The electrodissolution and passivation of mild steel in alkaline sulphide solutions at 25°C is investigated by the use of steady state and transient electrochemical techniques and by scanning electron microscopy and energy dispersive X-ray analysis. The electrodissolution and passivation processes are explained by the initial competitive adsorption of OH−, HS− and H2O and the subsequent charge transfer and proton transfer processes involving the OH and HS adsorbed species. The former is responsible for the passivation of the metal by an oxide metal layer while the second species undergoes two different reactions yielding in one case a precipitated mackinawite film on the metal, which is a poorly protective layer, and in the other a soluble Fe(II) species which can be detected by chemical analysis. The contribution of the reactions starting from each adsorbed species depends on the HS−/OH− concentration ratio in the solution. The initiation of pitting on iron is also explained through the postulated reaction pattern.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

The development of metal overlayers with smooth and rough topographies

A review of the recent advances made in the development of metal electrode surfaces with preferred crystallographic orientations and different roughnesses through the application of periodic potential treatments is presented. The different techniques are described for fcc metals in aqueous solutions with particular attention to platinum and gold. The probable mechanisms of the different electrochemical processes which are responsible for the changes in the surface structure of those metals are discussed. The possibility of modelling the growth of metal surface morphologies are considered as well as the importance of scanning tunneling microscopy imaging to assure the validity of proposed models.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

The development of metal overlayers with smooth and rough topographies

A review of the recent advances made in the development of metal electrode surfaces with preferred crystallographic orientations and different roughnesses through the application of periodic potential treatments is presented. The different techniques are described for fcc metals in aqueous solutions with particular attention to platinum and gold. The probable mechanisms of the different electrochemical processes which are responsible for the changes in the surface structure of those metals are discussed. The possibility of modelling the growth of metal surface morphologies are considered as well as the importance of scanning tunneling microscopy imaging to assure the validity of proposed models.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

The role of a slow phase formation process in the growth of anodic silver oxide layers in alkaline solutions—I. Electroformation of Ag(I) oxide layer

The anodic electroformation of silver (I) oxide layer on polycrystalline silver electrodes in 0.1 M NaOH was studied by using potentiodynamic and potentiostatic techniques. The growth of the silver oxide layer under a linear potential sweep or potential step measurements involves as a first step the electroformation of Ag2O or AgOH monolayer at potentials close to the Ag/Ag2O reversible electrode potential. This monolayer grows through a solid diffusion mechanism to form a 3-D primary silver (I) oxide. Subsequently the building up of a secondary silver (I) oxide layer is clearly noticed when the potential exceeds 0.24 V (vs sce). The formation of this layer can be described in terms of an instantaneous nucleation and 3-D growth mechanism under diffusion control. The ageing effects at the primary layer level decreases the nucleation rate so that for the growth of the secondary layer an intermediate situation between instantaneous and progressive nucleation under diffusion control can be observed. The secondary silver (I) oxide layer can be related to the aged silver (I) oxide species previously reported.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

An Interdisciplinary Approach to the Electrochemistry at Solid Electrodes

Um enfoque interdisciplinar na eletroquímica em eletrodos sólidos é apresentado levando-se em conta no vas interpretações básicas, tanto para o crescimento de fases quanto para a perturbação de fases sob condições longe do equilíbrio. Para esse propósito, os da dos de imagens derivadas de microscopia de tunelamento por varredura (STM) e de microscopia de força atômica (ATM) em diferentes escalas de comprimento, se tornam extremamente úteis. Esse enfoque proporciona no vas visões no desenvolvimento de rugosidade, decaimento de rugosidade e reatividade em eletrodos sólidos. O estudo de in ter faces móveis por aplicação sequencial de da dos de STM in situ e a interpretação baseada na teoria da escala dinâmica fornece uma descrição qualitativa e quantitativa das irregularidades da superfície, e provê informações sobre o mecanismo de evolução da in ter face sob re gimes estacionários e não-estacionários de rugosidade. Vários exemplos de interesse eletroquímico são discutidos na base deste enfoque interdisciplinar.An interdisciplinary approach to the electrochemistry at solid electrodes is presented here taking into account new basic interpretations for either phase growth or phase disruption under conditions far from equilibrium. For this purpose imaging data derived from scanning tunneling microscopy (STM) and atomic force microscopy (AFM) at different scale lengths are extremely useful. This approach provides new insights into roughness development, roughness decay and reactivity at solid electrodes. The study of mobile interfaces by the sequential application of in situ STM data and an interpretation based on the dynamic scaling theory furnish a qualitative and a quantitative description of surface irregularities, and provide information about the interface evolution mechanism under steady and non-steady roughness regimes. Various examples of electrochemical interest are discussed on the basis of this interdisciplinary approach.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Progress in the knowledge of irregular solid electrode surfaces

Modern approaches to solid surface disorder provide a more rigourous way of defining roughness at solid surfaces, a crucial concept in electrocatalysis. The study of this type of surface comprises growth kinetics, geometric description, relaxation kinetics and influence of surface irregularities on different reactions. Continuous rough columnar structured metal surfaces constitute a good model system for the investigation of a number of processes which are of special interest in heterogeneous catalysis, including electrocatalysis. The topography of these metal surfaces can be determined by scanning tunneling microscopy (STM) at different scales and can be described by means of the dynamic scaling theory applied to STM imaging. Roughness relaxation kinetics followed by electrochemical techniques can be interpreted through a coalescence-type mechanism. Typical examples of adsorption and diffusion controlled electrochemical reactions on this type of electrodes are presented.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada