Preparation and characterization of gold nanostructures of controlled dimension by electrochemical techniques

Gold sponges consisting of bicontinuous, 3D networks of branched nanowires and tortuous pores are prepared by anodic dissolution of silver from Ag75Au25 alloy sheets in 1 mol L-1 HClO4, an electrochemical process occurring under mixed charge transfer and mass transport control. Samples resulting from dissolution are characterized by SEM, which reveals different surface and bulk morphologies, and EIS that allows an estimate of the Au sponge surface area through the measurement of its double layer capacity. This capacity depends linearly on the dissolution charge and attains values of 3-10 Fg(-1) of gold, increasing for increasing dissolution potentials in the explored range. The relation between typical size of the nanostructures and measured capacity is discussed by reference to a simple geometrical model of the internal wire-like structure. Aging causes some capacity decay, to be attributed to slow coarsening processing.