36Cl labelling and electrochemical study of chloride adsorption on a gold electrode from perchloric acid media

Abstract

We present experimental data on adsorption of chloride anions on a smooth polycrystalline gold electrode using the ³⁶Cl radioactive labelling method. Owing to weak signal from the ³⁶Cl radiation source, previous radiochemical studies had been done with rough substrates. The radiochemical procedure includes the evaluation of a ‘squeezing efficiency’ and a contribution from secondary X-radiation, as well as a new calibration scheme vis-á-vis our previous efforts. Using this new radiochemical approach in combination with cyclic voltammetry, we studied the potential dependence of adsorption and surface–bulk exchange processes, and compared chloride and sulfate adsorption. In the double layer potential range, the already reported chloride surface concentration (Γ)–electrode potential relationships were confirmed. The Γ vs. E profiles taken in the oxidation range reflected a rich surface chemistry of gold in chloride media in terms of sorption properties of gold oxides and formation of gold complexes with chloride. An integrated understanding of chloride electrosorption and reactivity in the full electrode potential range accessible to investigations in aqueous solution is outlined based upon the experimental material obtained in this study.