Effect of Oxide Film Properties on the Kinetics of O2 Reduction on Alloy C-22

The kinetics of oxygen reduction on the Ni-Cr-Mo(W) Alloy C-22 in 5 M NaCl at 70 °C were studied using potentiostatic, voltammetric techniques, and electrochemical impedance spectroscopy. This research aimed to understand how the properties of the oxide film influence the kinetics of the O2 reduction process. It was found that oxygen reduction occurred at low potentials on defective oxide films with a high concentration of anion vacancies, involving a combination of 2-electron and 4-electron transfer mechanisms. At more positive potentials, a passive film was formed, leading to a CrIII-dominated barrier layer at the alloy/oxide interface and a Mo/W enriched outer layer at the oxide/solution interface, which suppressed oxygen reduction. Notably, the reduction process could be reinitiated following the transpassive degradation of the oxide film at more positive potentials, suggesting a catalytic effect on the MoVI/WVI surface film. These findings provide valuable insights into the electrochemical behavior of Alloy C-22 and its potential applications in environments susceptible to corrosion.