Structural Evolution of Au Electrodes during Cathodic Corrosion: Initial Stages of Octahedral-Nanocrystal Growth

Cathodic corrosion of Au wires in highly concentrated NaOH (5-20 M) is systemically investigated to monitor the structural transformation as a function of applied electrode potential, polarization time, and electrolyte concentration. Current -potential curves for the restructured Au electrodes in 0.1 M H2SO4 demonstrate preferential (111)-orientation of nanofacets and an increase in electrochemically active surface area as a function of the applied parameters. Scanning electron microscopy shows that polarizing the Au surfaces at sufficiently negative potentials leads to the growth of nanosized octahedral and triangular crystallites that can be tailored by varying NaOH concentrations. The nanocrystal growth occurs through dissolution and metal redeposition. The formation of etching pits indicates that Au dissolution is dominating during the initial stages of cathodic corrosion. The number of nanocrystals increases at more negative potentials due to the greater nucleation density induced by the higher concentration of dissolved Au species. Polarization times above 5.0 min result in fractal growth indicated by the appearance of multi-armed nanostructures. This work not only advances our understanding of the initial stages of nanocrystal formation but also offers a powerful means for controlling the shape and size of metal nanocrystals simply by the rational design of the cathodic corrosion.