Operando analysis of the electrosynthesis of Ag2O nanocubes by scanning electrochemical microscopy

The strategy proposed herein employs the scanning electrochemical microscope in generation/ collection mode to clarify the mechanism involved in the electrosynthesis of metal oxide nanoparticles, NPs. It offers simultaneously both generation of the precursors of the NPs and electroanalysis at a single NP level by nanoimpact coulometry. The former process is operated under controlled fluxes within the wide field of precursor diffusion in the inter-microelectrode gap, thus forming a tunable reaction layer allowing the growth of a size gradient of NPs within this gap. The latter process exploits the much slower diffusion of NPs, spatially frozen, in the near field of a collecting microelectrode. This then makes it possible to dynamically monitor the modes of growth of NPs in situ without perturbing their synthesis. As a proof of concept, the synthesis of Ag2O nanocubes, NCs, is described, using an Ag microelectrode to generate Ag+ ions while a facing Au microelectrode both electrogenerates HO and collects the resulting Ag2O NCs. Dynamic analysis of the NCs? reductive electrochemical impacts provides insights into their growth and stability. In particular, it suggests a two-step growth mechanism starting from the quasi-instantaneous nucleation of a > 260 nm nuclei followed by mass-transfer-driven crystallization over the nuclei.