The kinetics of oxygen reduction have been studied electrochemically on the Ni-Cr-Mo(W) Alloy C-22 in 5 M NaCl at 70 degrees C using potentiostatic and voltammetric techniques and electrochemical impedance spectroscopy. Oxygen reduction was observed to occur at low potentials on defective oxide films containing a high concentration of anion vacancies and appeared to proceed by a combination of 2-electron and 4-electron transfer processes. At more positive potentials a passive film comprising a Cr-III-dominated barrier layer at the alloy/oxide interface and a Mo/W enriched outer layer at the oxide/solution interface was formed, and oxygen reduction was completely suppressed. Oxygen reduction could be revived after transpassive degradation of the oxide film at more positive potentials, and appeared to be catalyzed on the Mo-VI/W-VI surface film. (c) The Author(s) 2017. Published by ECS. All rights reserved.