Natural Immersion Potentials of Gold and Platinum in Nitric Acid Solutions

Abstract

Potentials of inert metals immersed in nitric acid solutions, which are used in the reprocessing plants of spent nuclear fuel, have been considered to be useful as an index of redox properties of nitric acid solutions in which the various ions change their valency. We measured the immersion potentials of gold and platinum electrodes in (1~11) × 10₃ mol·m₃ nitric acid solutions at 25 and 75°C with and without the Ce₄₊/Ce₃₊Linear couple. Linear sweep voltammetry was carried out for these electrodes. The obtained potentials of the gold electrode were lower by about 0.15 V than the platinum potential for the corresponding conditions. The immersion potential of platinum was increased when the Ce₄₊/Ce₃₊ was added to the solution. The immersion potential of gold stayed constant when the Ce4+ concentration was less than 10 mol·m₃, while it increased when Ce₄₊ concentration was increased above that value. The voltammetry results suggested that there were surface species formation and water oxidation, including an adsorption process on the metal, occurring when gold and platinum were immersed, respectively. We concluded the immersion potentials were a mixed potential of these reactions and the redox reaction of ion couples in nitric acid solution.

KEYWORDS:

• redox potential
• immersion potential
• gold
• platinum
• electrode
• platinum electrode
• gold electrode
• voltammetry
• nitric acid
• pH values
• fission products
• spent fuel reprocessing