Electrocatalytic Metallic Nanostructures Prepared By Electrorefining and Cathodic Corrosion

Abstract

Metallic nanostructures (NS) due to their unique properties are often used as electrocatalytic electrode materials in energy conversion and storage as well as in sensing applications. Their common methods of preparation involve homogeneous synthesis and electrodeposition from solutions containing appropriate precursor and often reducing agent and capping agent (surfactant). The main drawbacks of these methods are restricted yield, waste production and often intrinsic contamination of the surface of obtained NS. Moreover, surface capping ligands affect electrocatalytic activity by hindrance of reactant access to the active sites.We propose a versatile method of preparation of bare (non-capped) mono- and multi-metallic (Au,1 Cu,2 Ag, Fe) NS by localized electrorefining of polycrystalline raw metals at high efficiency in a controlled manner. Catalytic activities of obtained NS towards oxygen reduction reaction (ORR) in alkaline media, hydrogen evolution (HER) and carbon dioxide reduction (CO2RR) to easily electrooxidizable fuels (formic acid and carbon monooxide) were analyzed by feedback mode scanning electrochemical microscopy (SECM). The morphology and specific activity of obtained NS depend on used support material (indium tin oxide (ITO) and glassy carbon) and other electrorefining parameters such as electrodeposition potential, source velocity and the composition of the electrolyte. The last parameter determines stoichiometry of Faradaic processes. Both gold and copper electrooxidation and electroreduction can follow one electron stoichiometry. ORR in alkaline media and CO2RR occur effectively on NS with highly developed surfaces, containing large number of defects, corners and edges, whereas HER occurs efficiently at crystallographic Cu facets. Bare gold NS also exhibit outstanding plasmonic properties. They were applied as support for surface-enhanced Raman spectroscopy (SERS) of single molecules providing enhancement factor >106.1 Another method of preparation of metallic nanostructures is cathodic corrosion. This approach for platinum was studied by Koper group.3 We used this procedure for platinum ultramicroelectrode treatment. Obtained Pt NS exhibit unique catalytic properties towards electrooxidation of glucose.