Pumping of Na+ onto a surface under electrochemical promotion conditions: a simulation study

MARIANA ISABEL ROJAS; MARCELO MARIO MARISCAL; EZEQUIEL PEDRO MARCOS LEIVA

Cancún, México

Congreso; International Materials Research Congress (IMRC XIX); 2010

International Materials Research Congress

PUMPING OF Na+ ONTO A O-p(2x2)-Pt(111) SURFACE UNDER ELECTROCHEMICAL PROMOTION CONDITIONS: A SIMULATION STUDY   M.I.Rojas, M.M. Mariscal, E.P.M. Leiva Departamento de Matemática y Física, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, 5000 Córdoba, Argentina. E-mail: eleiva@fcq.unc.edu.ar   The catalytic activity of the some metallic surfaces deposited on solid electrolytes, may be reversibly decreased or accelerated by means of the electrochemical pumping of ions to the catalyst/gas interface (c/g). When aconductor electrolyte is employed like , the negative polarization of the electrode leads to the migration of strongly polarized metal atoms usually represented as. Thus, an effective double layer is established, modifying the work function of the metal exposed, and affecting the binding strength of reacting adsorbed molecules. The change in the surface dipole of the catalyst, becomes manifest in changes in the surface catalytic activity that are reversible and even predictable on the basis of models [1-3]. In the present work we perform Monte Carlo simulations on the adsorption of ions on a charged surface, so as to emulate the formation of the above mentioned electrostatic double layer. The computer simulation is performed in the Grand Canonical ensemble, where the chemical potential of the adsorbed species, the volume of the system and the temperature are fixed, in order to represent the experimental boundary conditions. Theand substrate interactions were fitted from DFT calculations employing SIESTA computer code [4]. In the present work we study the pumping of  atoms onto a  surface as a function of the chemical potential applied within the rangeeV. First, at very low coverages, the film presents a disordered structure, then a becomes evident and at  a ordered structure occurs. These expanded structures are due to the strong repulsive lateral interaction between Na+ adatoms, and the latter is the same as that observed experimentally by STM [5]. We can conclude that the simple computational model presented in this work is able to predict an important number of qualitative features of the properties found in the experiments, opening new perspectives for the simulation of the effective double layer occurring in NEMCA and other related phenomena.     [1] C.G. Vayenas, S. Bebelis, I.V. Yentekakis, en: G. Erlt, H. Knötzinger, J. Weitcamp (Eds.) Handbook of Catalysis, VCH, Weinheim, 1997, 1310-1338. [2] C. Vayenas and S. Brosda, Solid State Ionics 154-155 (2002) 243. [3] G. Vayenas and S. Brosda and C. Pliangos, J. Catal. 216 (2003) 487. [4] J.M. Soler, E. Artacho, J.D. Gale, A. García, J. Junquera, P. Ordejón, D. Sánchez-Portal, J. Phys.: Condens. Matter 14 (2002) 2745-2779. [5] M. Makri, C.G. Vayenas, S. Bebelis, K.H. Besocke, C. Cavalca, Surface Science 369 (2001) 351-359.