Nanoporous Gold Formation by Free Corrosion Dealloying of Gold-Silver Alloys in Nonoxidizing Acids Driven by Catalytic Oxygen Reduction Reaction

Abstract

Highly concentrated nitric acid (molarity ~ 15 M), a strong oxidizing agent, has been extensively used to produce nanoporous gold by free corrosion dealloying of gold-silver alloys. This is because, kinetically, silver dissolution in dilute nitric acid with molarity 5 M (or lower) is not favorable at ambient temperature and pressure. We recently reported (Deng and Detsi in Nanoscale 9:11858, 2017; Fu et al. in ACS Appl Nano Mater 1(8):4164, 2018) on the use of catalytically driven reduction reactions to enhance the rate of nanoporous silver and nanoporous gold formation at ambient temperature and pressure by free corrosion dealloying in hydrochloric acid, a nonoxidizing acid. Here, we further elucidate these findings by combining our experimental studies with the mixed potential theory of corrosion to shed more light on the reaction mechanisms associated with free corrosion dealloying of silver-aluminum alloys, and gold-silver alloys in various corroding media and in the presence of a catalyst used to enhance the dealloying rate.