ELECTROCHEMICAL DESORPTION AND ADSORPTION OF NONYL MERCAPTAN AT GOLD SINGLE-CRYSTAL ELECTRODE SURFACES

The electrochemical behavior of a nonanethiol layer adsorbed an Au(111 ), Au(110), and on a Au polycrystal has been examined using cyclic vol tammetry. The reductive desorption and the oxidative redeposition of t he nonanethiol molecules at the Au(111) surface have been shown to dep end strongly on the pH of the electrolyte solutions. While the amount of material reductively desorbed from the surface on the first cathodi c cycle is independent of the pH, the amount of material that is oxida tively redeposited increases significantly as the pH is lowered. This behavior is ascribed to a reduction in solubility of the product of de sorption (thiolate or thiol) as pH decreases. At high pH the redeposit ion of the layer seems to occur in one step, but at pH values that are lower than the pK(a) of the nonanethiol the redeposition seems to occ ur in two steps. In an alkaline solution, the reductive desorption of the nonanethiols from a Au(110) surface is similar to the same process at the Au(111) surface. The double layer charging current, the shape of the reductive current peaks, and its integrated charge are similar to those measured on the Au(111) electrode. Our single crystals study also reveals a correlation between the potential of zero charge of the uncoated gold, single crystal electrodes and the potential at which t he reductive desorption of the nonanethiols occurs. The results on a p olycrystalline surface indicate a complex stripping patten that is rel ated to the different crystallographic domains present on the polycrys talline electrode.