Shape- and size-selective electrochemical synthesis of dispersed silver(I) oxide colloids

Silver(I) oxide ((AgO)-O-2) micro- and nanoparticles were electrochemically synthesized by anodizing a sacrificial silver wire in a basic aqueous sulfate solution. Ag2O particles were released from the silver electrode surface during synthesis producing a visible sol "stream". The composition of these particles was established using selected area electron diffraction, X-ray diffraction, and X-ray photoelectron spectroscopy. The shape of Ag2O crystallites could be adjusted using the potential of the silver wire generator electrode. The generation of a dispersed Ag2O sol and the observed shape selectivity are both explained by a two-step mechanism involving the anodic dissolution of silver metal, Ag-0 -> Ag+(aq) + 1e(-), followed by the precipitation of (AgO)-O-2 particles, 2Ag(+) + 20H(-) -> Ag2O(s) + H2O. Within 100 mV of the voltage threshold for particle growth, cubic particles with a depression in each face ("hopper crystals") were produced. The application of more positive voltages resulted in the generation of 8-fold symmetric "flower"-shaped particles formed as a consequence of fast growth in the (111) crystallographic direction. The diameter of flower particles was adjustable from 250 nm to 1.8 mu m using the growth duration at constant potential.