Tuning the morphology and chemical distribution of Ag atoms in Au rich nanoparticles using electrochemical dealloying.

Abstract

Dealloying of Ag-Au alloy nanoparticles (NPs) strongly differs from the corresponding bulk alloy materials. Here, we have investigated the effects of potentiodynamic and potentiostatic dealloying on structure and distribution of residual Ag atoms for Au rich NPs. Two different sizes of Ag rich alloy NPs, 77 ± 26 nm Ag77Au23 and 12 ± 5 nm Ag86Au14, were prepared. 77 nm Ag77Au23 NPs form a homogeneous alloy, while 12 nm Ag86Au14 NPs show an Ag rich shell-Au rich core arrangement. The two groups of as-prepared NPs were dealloyed either under potentiodynamic (0.2-1.3 VRHE) or potentiostatic (0.9, 1.2, and 1.6 VRHE) conditions in 0.1 M HClO4. For the initial 77 nm Ag77Au23 NPs, both dealloying protocols lead to pore evolution. Interestingly, instead of homogenous Ag distribution, numerous Ag rich regions form and locate near the pores and particle edges. The critical dealloying potential also differs by ∼500 mV depending on the dealloying method. The initial 12 nm Ag86Au14 NPs remain dense and solid, but Ag distribution and thickness of the Au passivation layer vary between both dealloying protocols. When the Au passivation layer is very thin, the residual Ag atoms tend to segregate to the particle surface after dealloying. Due to the size effect, small NPs are less electrochemically stable and show a lower critical dealloying potential. In this systematic study, we demonstrate that the mobility of Au surface atoms and dealloying conditions control the structure and residual Ag distribution within dealloyed NPs.