Study of adsorption and oxidation of thiocyanate at the metal / solution interface by EQCM and EIS

Thiocyanate (SCN^-) is widely used in industrial and scientific areas; nevertheless, few studies have been made to understand the mechanism of adsorption and electrochemical oxidation of SCN^-. This work shows the results of a study of the adsorption and oxidation of SCN^- at different concentrations on a Pt electrode in a 0.1M HClO₄ electrolyte solution. In the behavior of this system, studied with an Electrochemical Quartz Crystal Microbalance (EQCM) coupled with Cyclic Voltammetry (CV), we observed an irregular tendency of anodic current with respect to the concentration of the additive. To understand this, we used Electrochemical Impedance Spectroscopy (EIS), testing four different reaction mechanisms that involve the adsorption and oxidation of thiocyanate. For each one of the tested mechanisms a transfer function was proposed and fitted to the experimental data. According to the pattern recognition method, the best fitted mechanism involves the formation of (SCN)₂ as an intermediate. copyright The Electrochemical Society.