An SFG investigation of Au(1 1 1) and Au(2 1 0) 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(1 1 1) and Au(2 1 0) 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. Spectroelectrochemical results were complemented with cyclic voltammetric measurements. The nature and potential dependence of the CN− adsorbed onto Au(2 1 0) are not measurably affected by the presence of CPC in the electrolyte. On the contrary, with the Au(1 1 1) 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(2 1 0) surface is not appreciably influenced by the presence of cetylpyridinium, while the more loosely bound species present on Au(1 1 1) are affected by coadsorption.