Kinetically Controlled Growth of Fine Gold Nanofractals from Au(I) via Indirect Galvanic Replacement Reaction

Two of the most important features of Au nanostructures, size and shape, are significantly affected by the reduction kinetics of the relevant metal precursors. Because of the high standard oxidative potential of gold ionic species, AuCl4- in particular, Au fractals formed via various chemical or electrochemical approaches often have very coarse branches with diameters varying from tens of nanometers to submicrometers, even though extensive chemicals and/or complicated processes have been deployed to control the reduction kinetics. Herein we report an indirect galvanic replacement (IGR) strategy where the electrons generated in a galvanic replacement reaction from anode oxidation are channeled out to a separate conducting film on which the cathodic metal can be deposited. Reduction of Au(I) ionic species with relatively low standard oxidative potential has been conducted with the IGR experimental setting. 2D finely hyperbranched Au fractals (4.0 nm in diameter and a few micrometers in length) with high structural integrity were produced. Controls over the deposition density, location, and microfeatures of Au nanofractals were demonstrated through a mechanistic study. In addition, the thus-prepared Au nanofractals were also thoroughly tested in electrochemical sensing of H2O2.