A Comparative Study on Gold and Platinum Dissolution in Acidic and Alkaline Media

Abstract

Electrochemical dissolution of gold and platinum in 0.1 M HClO4, 0.1 M H2SO4, and 0.05 M NaOH is investigated. The qualitative picture of both metals’ dissolution is pH-independent. Oxidation/reduction of the metal's surface leads to the transient dissolution peaks which we label A1 and C1 on the dissolution profiles. Commencement of the oxygen evolution reaction (OER) results in the additional dissolution peak A2. Quantitatively, there are important differences. The amount of gold transiently dissolved in alkaline medium is more than an order of magnitude higher in comparison to that in acidic medium. Oppositely, steady-state gold dissolution in base in the potential region of OER is hindered. The transient dissolution of platinum is by a factor of two higher in base. It is suggested that variation of the pH does not change the mechanism of the OER on platinum. Consequently, the dissolution rate of platinum is equal in acidic and alkaline electrolytes. As an explanation of the observed difference in gold dissolution, a difference in the thickness of compact oxide formed in acid and base is suggested. Growth of a thicker compact oxide in the alkaline medium explains the increased transient and the decreased steady-state dissolution of gold.