Search

An overview is given of selected theoretical, experimental and computer simulation research on thermodynamic modeling applied to the metal underpotential deposition. Focus is made mainly on the last 20 years. The upd -theory on planar surfaces is revisited and the thermodynamic framework is extended to consider underpotential deposition on nanoparticles and to include anion coadsorption, solvation and double layer charging. Results from molecular dynamics and Monte Carlo simulations are shown for systems of experimental interest. At the end some perspectives for further advanced modeling of the present problem are given. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical decoration of Au and Pd nanoparticles by Pd and Au atoms respectively is discussed in a statistical mechanical framework. It is found that depending on precursor nanoparticle size and shape, controlled decoration may be achieved in undersaturation or oversaturation conditions. Multilayer deposition is also considered, with the finding that this phenomenon is also size dependent. [Copyright &y& Elsevier]

Abstract: A thermodynamic model predicting the disappearance of the underpotential deposition phenomenon in the limit of small nanoparticles is proposed and developed for selected families of geometric bodies. The key parameters are the binding energy of adatoms on the flat foreign substrate and at the edges of the nanoparticle. [Copyright &y& Elsevier]

Abstract: The meaning of underpotential shift is discussed for free nanoparticles, where a redox couple is used to set potential control on them. Atomistic Monte Carlo simulations are performed to study their decoration in the submonolayer regime. The resulting configurations are used to simulate their plasmon spectra by means of a state-of-the art quantum mechanical atomistic model. [Copyright &y& Elsevier]

Abstract: In the present work we discuss the statistical mechanical framework for predicting the decoration of metallic nanoparticles using electrochemical methods, in thermodynamic equilibrium. It is found that depending on the interactions between the two metals, controlled decoration may be achieved for core–shell nanoparticles in undersaturation and oversaturation conditions. The concept of underpotential deposition is discussed for the case of nanoparticles, with the finding that this phenomenon may be size dependent. [ABSTRACT FROM AUTHOR]

Abstract: The energetic stability of a set of 36 adsorbate/substrate(111) couples involving Au, Ag, Cu, Ni, Pt, and Pd is analyzed for perfect metal surfaces and metal surfaces with different types of defects. Monte Carlo annealing at low temperatures is performed to obtain the minimum energy configurations. The simulation results are used to check some theories employed to calculate the binding energy of atoms on surfaces from simple energetic considerations. Besides, a new phenomenological formulation is developed, which can be employed to predict the existence of underpotential deposition for several types of 0-dimensional structures. [Copyright &y& Elsevier]

Abstract: Electrochemical deposition of a metal on a foreign substrate may occur before or after the Nernst reversible potential, depending on the chemical nature of the substrate and adsorbate in question. Statistical mechanical treatment and a proper description of interactions between the particles of the system are necessary for an adequate theoretical representation of the electrochemical systems. In the present work, changes in relevant thermodynamic properties due to adsorption of a metal on a foreign single crystal (h k l) metallic surface are studied for a number of systems of electrochemical interest by means of quasi-harmonic (QH) lattice dynamics calculations with embedded atom method potentials at 300K. The metal couples considered involve silver, gold, platinum, palladium and copper. Underpotential and overpotential deposition trends observed for this set of transition metal systems are analyzed taking into account the changes in the internal energies and the entropic contributions due to deposition processes. The possibility of obtaining entropic information from measurements at different temperatures is also discussed. [Copyright &y& Elsevier]

Abstract: In order to contribute to the understanding of metal electrodeposition on real surfaces, we consider in the present work the deposition of Ag, Cu and Pd on a Pt(111) surface with defects. Off lattice Monte-Carlo simulations were performed using embedded atom method Potentials in the canonical ensemble at 300 K. Structural and energetic properties of deposits on surface defects of low dimension (iD=0,1,2) were studied. Among others, we consider vacancies (0D), steps (1D) and holes (2D). The results obtained are in qualitative agreement with experimental data in the literature. [Copyright &y& Elsevier]

The voltammetric behavior of Li+ intercalation/deintercalation in/from LiMn2O4 thin films and single particles is simulated, supporting very recent experimental results. Experiments and calculations both show that particle size and geometry are crucial for the electrochemical response. A remarkable outcome of this research is that higher potential sweep rates, of the order of several millivolts per second, may be used to characterize nanoparticles by voltammetry sweeps, as compared with macroscopic systems. This is in line with previous conclusions drawn for related single particle systems using kinetic Monte Carlo simulations. The impact of electrode kinetics and finite space diffusion on the reversibility of the process and the finiteness of the diffusion in ion Li / LiMn2O4 (de)intercalation is also discussed in terms of preexisting modeling. [ABSTRACT FROM AUTHOR]

Kinetic Monte Carlo simulations are applied to simulate the insertion of lithium ions into graphite. The present results show how the kinetics of lithium ion intercalation in graphite rules the global process, leading to metastable phases. The relatively slow rate of the events of insertion (deinsertion) of lithium ions into (from) graphite is found to yield the intercalation structures proposed by Daumas and Hérold. These arrangements can be considered as frustrated, metastable structures, with a higher energy than that of the equilibrium state. [ABSTRACT FROM AUTHOR]

To delve deeper into the kinetics involved in the staging phenomena of lithium insertion into graphite, it is necessary to develop theoretical models that emulate the physical phenomenon involved. In the present work kinetic Monte Carlo simulations are used to carry out a thorough analysis of the Li-ion graphite system, with the twofold aim of providing atomistic support for interpretations based on several experimental electrochemical techniques commonly used in the laboratory and of making theoretical predictions for future experimental work. Cyclic voltammograms and chronoamperometric transients are obtained, and diffusion coefficients and exchange current densities are calculated at different Li loadings of graphite. These results are compared with selected experimental data from the literature. In this way, there emerge details that cannot be observed in ordinary experiments due to methodological/instrumental limitations. For example, it is found that chronoamperometric responses are different for intercalation and deintercalation, the latter being a faster process. The reason why these phenomena are different is revealed, supporting and widening experimental assumptions. The present results also suggest that the intrinsic hysteresis observed in experimental work (and in simulations) is due to kinetic factors. • Kinetic Monte Carlo simulations emulate electrochemical techniques allowing a deep atomistic study. • Cyclic voltammetry and chronoamperometric simulations profiles provide understanding on experimental results. • Diffusion coefficients and exchange current density predict the behavior of Li-ion in different intercalation levels. • Deintercalation is faster than intercalation, due to the Li-ion clog next to the interphase in the lithiation. • The hysteresis phenomenon is apparently related to a kinetic origin. [ABSTRACT FROM AUTHOR]