The cathodic polarization characteristics of CuO and YBa2Cu3O7-delta electrodes were studied in the temperature range 600 to 800 degrees C and at oxygen partial pressures ranging from 10(-4) to 0.21 atm. The activity of oxygen reduction on a CuO electrode is closely related to the electronic conductivity and the oxygen ion vacancy density in the surface layer of the electrode. The oxygen ion vacancies created in CuO by doping with Li and the modification of the electronic conductivity by adding Ag provide a new way of enhancing the activity of an oxide electrode for oxygen reduction. It is demonstrated that the rate limiting steps for oxygen reduction at high overpotential and low overpotential are oxygen adsorption and charge transfer on CuO, respectively.