Adsorption of the formyl species on transition metal surfaces

J. R. B. Gomes* and J. A. N. F. Gomes

CEQUP/Dept. de Química, Faculdade de Ciências da Universidade do Porto,

Rua do Campo Alegre, 687, 4169-007 Porto, Portugal

The electrocatalytic oxidation of small organic species, namely methanol and its reaction intermediates, at transition metal and related surfaces has long been a subject of widespread practical as well as fundamental interest given its importance in fuel-cell research [1]. The central issue for such systems is the nature of the adsorbed species present under reaction conditions and, particularly, their role as reaction intermediates or poisoning species. One of these intermediates is the formyl species, HCO, which was proposed for the methanol oxidation reaction on several transition metal surfaces. In the electrochemical oxidation of methanol, HCO was proposed as a reactive intermediate on Pt, Ag and Au surfaces. This species is formed from adsorbed formaldehyde and, in alkaline media, is thought to be the reactant for the formate production written as follows:

HCO_(ads) + OH_(ads) -> HCOOH 1

HCOOH + OH^- -> HCOO^- + H₂O 2

It has been also proposed that this reactive intermediate is involved in the formation of poisoning species. The poisoning species are oxidised to CO₂ at potentials higher than 0.72 eV as follows:

HCO -> poisoning species + nOH_(ads) -> CO₂ 3

In this poster, we will present results from density functional theory calculations concerning the adsorption of the formyl species on copper, gold and platinum surfaces [2]. Four different adsorption sites on the (111) surfaces were considered. Calculated vibrational frequencies are in good agreement with previous theoretical and experimental data [3].

[1]- R. Parsons, T. VanderNoot, J. Electroanal. Chem. 1998, 257, 9.

[2]- J. R. B. Gomes, J. A. N. F. Gomes, J. Electroanal. Chem., in press.

[3]- Y. Zhang, M. J. Weaver, Langmuir 1993, 9, 1397.