Electrochemical Dealloying of Gold-Silver Nanoparticles - Selective Dissolution of the Less and More Noble Species

Abstract

Gold-silver alloy nanoparticles (NPs) capped with adenosine 5'-triphosphate with average diameters ~4 nm were immobilized into layer-by-layer (LbL) films deposited on indium-tin oxide (ITO) electrodes. Irreversible oxidative dissolution (dealloying) of the less noble silver atoms from the alloy NPs was performed by cyclic voltammetry (CV) in sulfuric acid. Alloy NPs with higher gold content required larger overpotentials for silver dealloying. Dealloying of the more-noble gold atoms from the alloy NPs was also achieved by CV in sodium chloride. The silver was oxidized first to cohesive silver chloride, and then gold dealloying to soluble HAuCl4 - occurred at higher potentials. Silver oxidation was inhibited during the first oxidative scan, but subsequent cycles showed typical, reversible silver-to-silver chloride voltammetry. The potentials for both silver oxidation and gold dealloying also shifted to more oxidizing potentials with increasing gold content, and both processes converged for alloy NPs with >60% gold content.