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 HAuCl 4 -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.

Disproportional surface segregation in ligand-free gold–silver alloy solid solution nanoparticles, and its implication for catalysis and biomedicine

“…This third peak is characteristic of AgAu alloys. As the nanoparticle sizes were in a similar range, this peak cannot be attributed to a size effect but rather to the oxidation of silver, whose activity has been decreased due to the stabilization by the gold matrix 52,54 , a phenomenon previously observed in leaching experiments with AgAu single particles analysed by hyperspectral spectroscopy 14 . An explanation for the missing of this reaction in Ag50Au50 is the higher thermodynamic stability of the equimolar compositions, as discussed above, which would inhibit complex oxidation processes.…”

Surface Facet Engineering in Nanoporous Gold for Low-Loading Catalysts in Aluminum–Air Batteries

“…Next, we fabricated electrolytically dealloyed npAu on carbon paper, which we called Elec-npAu-citrate, through electrochemical dealloying of the Ag 75 Au 25 leaves laminated on carbon paper in a 0.1 M sulfuric acid aqueous solution with and without sodium citrate under 0.7 V vs Ag/AgCl for 12 h using a three-electrode system at room temperature (Figure 1B). 53 In a typical synthesis procedure, we used three layers of 100 nm-thick Ag 75 Au 25 leaves laminated on carbon paper as a working electrode, a platinum plate as a counter electrode, and Ag/AgCl as a reference electrode in a home-built cell (Figure S1). The electrolyte was 0.1 M sulfuric acid with 2 mg/mL of sodium citrate (batch 1) and without sodium citrate (batch 2).…”

Comparison of 20 nm silver nanoparticles synthesized with and without a gold core: Structure, dissolution in cell culture media, and biological impact on macrophages

“…Au-Ag alloys are a classic system for examining dealloying effects because only Ag dissolves. 70,71 However, galvanic corrosion occurs when both metals are exposed to the solution, which was not the case for the assynthesized particles. In a study of dealloying of Au-Ag alloy nanoparticles, Star and Buttry 71 noted that an over potential was required to remove the Ag from these alloys and a subset of Ag atoms appeared to be protected by Au in the NP cores.…”