Energetic and entropic contribution to the underpotential deposition shift on monocrystalline surfaces
O.A. Oviedo, M.I. Rojas, E.P.M. Leiva
INFIQC, Unidad de Matemática y Física, Facultad de Ciencias Químicas,
Universidad Nacional de Córdoba, 5000 Córdoba, Argentina
The electrochemical deposition of a metal on a surface of different nature can occur before or after the Nernst?s reversible potential. This phenomena depends on the chemical nature of the substrate and adsorbate in question. An adequate theoretical representation of the real electrochemical systems require of a statistical mechanical treatment of them, as well as a proper description of the interactions between the particles of the system.
The potential shift in the canonic ensemble (NVT) can be calculated as
where 
, 
, 
, 
, 
and 
are the Helmholtz free energies, internal energies and entropies of adsorption of 
on and the adsorption of on 
, respectively, and we have neglected the volumen changes of the system. The changes in the Helmholtz energy 
, internal energy 
and the entropic contribution 
due to the adsorption of a metal (of equal or different nature) on a monocrystalline (hkl) metallic surface was studied for a number of systems of electrochemical interest. The metal couples considered involve silver, gold, platinum, palladium and copper. We have performed quasi-harmonic lattice dynamics (EAMLD) [1-2] calculations with embedded atom method potential (EAM) [3] at 300 K. This allowed us to evaluate the entropic contribution due to the metallic deposition for a series of systems of electrochemical interest. The underpotential and overpotential deposition trends observed for this set of transition metal systems are analyzed taking into account the changes of the internal energies and the entropic contributions due to the deposition processes.
References
[1] G.D. Barrera, R.H. de Tendler, E.P. Isoardi, Modelling Simul. Mater. Sci.
[2] G.D. Barrera, R.H. Tendler, Comput. Phys. Commun 105 (1997) 159.
[3] S. M. Foiles, M.I. Baskes, M.S. Daw, Phys. Rev. B 33 (1986) 7983.
