(Digital Presentation) Investigation of the Hexylamine Adsorption on Platinum By Potentiostatic and Potentiodynamic Methods

Abstract

Adsorption is one of the electrochemical process stages often. The adsorption of polar organic molecules (surfactants) on metal electrodes is of significant interest. In particular, the surfactant adsorption affects the exchange current value and determines the metal corrosion rate. Therefore, the explanation of the adsorption mechanism is the most important problem in the investigation of the electrochemical kinetics.The kinetics of the Fe2+ and Fe3+ oxidation-reduction reaction on a platinum electrode in 1 M HClO4 was investigated by potentiodynamic and chronoamperometric methods in the presence of hexylamine as a surfactant. The main kinetic characteristics of the reaction (exchange current density, transfer coefficient, diffusion coefficients of iron ions) have been determined.The dependence of the exchange current density on the hexylamine concentration is analyzed. The surface coverage with a surfactant was estimated at various hexylamine concentrations. It was shown that the hexylamine adsorption on platinum is described by the Dhar-Flory-Huggins adsorption isotherm. The values of the adsorption constant and the adsorption free energy are obtained. These values are close to the corresponding values for the hexylamine adsorption on mild steel in hydrochloric acid. Consequently, the objective laws for the hexylamine adsorption depend low on the acid type and the electrode nature. This indicates the physical adsorption of the surfactant.It is possible that adsorption occurs due to the hydrophobic interaction of the surfactant molecules with polar water molecules. Then, the displacement of surfactant molecules to the interface takes place regardless of the nature of the acid and the metal contacting with the solution. The latter assumption requires further investigations of the surfactant adsorption on various metals.