Electrochemical behavior of copper metal core/oxide shell ultra-fine particles on mercury electrodes in aqueous dispersions

Methods of voltammetry and polarography have been applied to study electrochemical behavior of ultrafine copper particles with Z-average diameter ∼120 nm in aqueous electrolytic media on mercury electrodes. Particles have been preliminarily stabilized by controllable passivation at low partial pressures of oxygen what resulted in formation of superficial oxide shell with certain composition and structure. It has been found that special electrochemical behavior of the particles in aqueous media is caused by the size effects as well as by the processes (partial dissolution, complexation) occurring at the “particle/solution” interface. Electroreduction of the dispersions takes place at about –0.8 V (Ag/AgCl/KCl sat.). The mechanism of electroreduction includes an adsorption stage due to electric charge which the particles bear in the electrolyte. The particle adsorption on the electrode has been shown by differential capacity measurements, the surface charge in different electrolytes was estimated by means of potentiometric titration of the dispersions. The sign of the charge and the probable electroactive species formed by partial dissolution of CuO and Cu2O in the electrolytic medium have been considered on basis of equilibria at the copper particle/dispersion interface.