Electrochemical Behavior of Copper in Aqueous Solutions Under Industrial-Frequency Alternating Current Polarization

The electrochemical behavior of copper under industrial-frequency (50 Hz) alternating current polarization was investigated in sulfate- and chloride-containing aqueous solutions using Cu-Cu and Cu-Ti electrode pairs. Copper–copper pairs showed practically no directional electrochemical processes, whereas replacing one electrode with titanium caused copper oxidation owing to a passive TiO2 film that forms on the titanium surface during the anodic half-cycle and acts as a rectifier. By varying the electrolyte composition (H2SO4, Na2SO4, HCl, NaCl), current density (from 2 × 104 to 1.5 × 105 A·m−2) and Cu2+ concentration (5–30 g·L−1), different copper compounds could be synthesized selectively and with high current efficiency: copper(II) oxide (CuO) formed in Na2SO4 (current efficiency up to 89.2%), metallic copper powder formed in H2SO4 containing Cu2+ (up to 75.2%), copper(I) oxide (Cu2O) formed in NaCl (99.1%), and copper(I) chloride (CuCl) formed in HCl with an apparent current efficiency exceeding 100% owing to concurrent processes.