Study of gold electrodissolution by scanning electrochemical microscopy in different modes

The electrodissolution of gold has already been widely studied by several methods, but no consensus concerning the reaction mechanism has been reached. In this work, the scanning electrochemical microscopy (SECM) has been used in transient condition for studying the electrodissolution of gold in H2SO4 solutions, with different concentration of chloride added, in order to elucidate the elementary steps of this mechanism. The electroactive species generated during Au dissolution, namely AuCl2-, AuCl3- and AuCl4-, were detected using a Pt microelectrode positioned at various distances from the Au electrode. Additionally, the SECM in transient mode (AC-SECM), which allows several transfer functions to be determined, has been used to characterize the presence and the relaxation time-constants of adsorbed intermediates formed at the Au electrode during its dissolution. The interpretation of the results is presented and discussed according to the different mechanisms reported in the literature, and subsequently, a new reaction mechanism is proposed.