Voltammetric characterization of oxide films formed on copper in air

Oxide layers thermally formed on copper have been studied using double swee p cyclic voltammetry in strongly alkaline electrolytes. It was found that t he addition of 1 M LiOH in an electrolyte (6 M KOH) allowed perfect resolut ion of cathodic waves due to the reduction of Cu2O and CuO. Assignment of t he two reduction waves has been achieved with the help of spectrophotometri c techniques including X-ray photoelectron spectroscopy and X-ray diffracti on; the cathodic wave appearing between -1.3 and -1.5 V (vs. Ag/AgCl) was a ttributed to the reduction of Cu2O, while that appearing at a less negative potential (-1.0 to -1.1 V) was attributed to the reduction of CuO. The ele ctrochemical measurement of samples prepared under several conditions has r evealed that CuO is reduced at once to Cu prior to the reduction of Cu2O. I t was also confirmed that the formation of the oxide films was accelerated by elevating temperature, heightening humidity, and by preimmersion in elec trolyte solutions. Water vapor was essential for the formation of CuO at a lower temperature (80 degreesC). (C) 2001 The Electrochemical Society.