The Oxygen Evolution Reaction Drives Passivity Breakdown for Ni-Cr-Mo Alloys

Area of Science:

• Materials Science
• Electrochemistry
• Corrosion Science

Background:

• Metallic material lifetime is limited by corrosion, particularly the challenging study of passive films at metal-liquid interfaces.
• Ni-Cr-Mo alloys are vital in industrial applications but susceptible to corrosion.
• Understanding passive film breakdown is crucial for predicting and preventing material degradation.

Purpose of the Study:

• To investigate the mechanism of passive film breakdown in a Ni-Cr-Mo alloy.
• To elucidate the role of the oxygen evolution reaction (OER) in corrosion.
• To differentiate the breakdown mechanism from typical transpassive dissolution.

Main Methods:

• Combined use of synchrotron-based techniques and electrochemical methods.
• Investigation of passive film behavior under anodic potentials.
• Analysis of metal dissolution and surface processes.

Main Results:

• The Ni-Cr-Mo alloy is active towards the oxygen evolution reaction (OER).
• OER onset correlates with passivity loss and significant metal dissolution.
• Passivity breakdown is driven by Mo oxidation (Mo4+ to Mo6+) and subsequent dissolution, not Cr6+ release.

Conclusions:

• The oxygen evolution reaction (OER) plays a critical role in the passivity breakdown of Ni-Cr-Mo alloys.
• OER-induced surface acidification accelerates metal dissolution at high current densities.
• The catalytic activity of these alloys in OER must be considered in corrosion studies.