Monte Carlo simulations of the adsorption of ionic species at the catalist/gas interface

C. VAZQUEZ; M. M. MARISCAL; E. P. M. LEIVA

Banff, Canada

Congreso; 58th Annual Meeting of the International Society of Electrochemistry; 2007

ISE

The catalytic activity of metal films deposited on solid electrolytes may be drastically modified in a reversible way by means of the application of current or a potential difference between the metal catalyst and a counter electrode. This phenomenon, know as Non- Faradaic Electrochemical Modification of Catalytic Activity, NEMCA) [1], has been the subject of extensive experimental and theoretical research.

When a current density is allowed to flow between the catalyst and the counter electrode, depending on the sign of the current, anions or cations migrate from(or to)the solid electrolyte towards(from) to the catalyst surface, in a process known as back spillover. Thus, an effective double layer is established, which modifies the work function of the metal exposed, and affects the binding strength of reacting adsorbed molecules. The change in the surface dipole of the catalyst, manifest in the change of the work function of the system, produces remarkable changes in the surface catalytic activity that are reversible and even predictable on the basis of models[2-4].

In the present work we perform Monte Carlo simulations on the adsorption of ions on a charged surface, so simulate the formation of the above mentioned electrostatic double layer. The computer simulation is performed in the Grand Canonical ensemble, to emulate the experimental boundary conditions. The metal is represented as a perfect conductor and the ions interact with the surface through their image charge.

The structure of the system, the coverage degree and the surface dipole are analyzed as function of the chemical potential, comparing the predictions of the model with experimental results.

 

[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, S. Brosda and C. Pliangos, J. Catal. 216(2003)487.

[4] C.G. Vayenas, Solid Sate Ionics, 198 (2004) 321.