An SFG investigation of Au(111) and Au(210) electrodes in aqueous solutions containing KCN and cetylpyridinium chloride

Cetylpyridinium chloride (CPC) is known to affect electrocrystallisation processes in the presence of cyanide; this behaviour is believed to be due to surface-specific differences in coadsorption properties. In this paper, the behaviour of Au(111) and Au(210) electrodes in contact with neutral aqueous solutions of KCN in the absence and in the presence of CPC has been studied as a function of potential by means of sum frequency generation (SFG) spectroscopy. The potential-dependent CN- stretching band position has been followed. Spectroelectrochernical results were complemented with cyclic voltammetric measurements. The nature and potential dependence of the CN- adsorbed onto Au(210) are not measurably affected by the presence of CPC in the electrolyte. On the contrary, with the Au(111) surface, two CN--related bands appear, due to adsorbed cyanide and ionic cyanide present at the surface, respectively. This phenomenon might be linked to the formation of surface ion pairs occupying a fraction of the electrode surface. These SFG results have thus disclosed that the more strongly bound CN- onto the more open Au(210) surface is not appreciably influenced by the presence of cetylpyridinium, while the more loosely bound species present on Au(111) are affected by coadsorption. (C) 2004 Elsevier B.V. All rights reserved.