In this work, elementally resolved electrochemical technique, namely atomic emission spectroelectrochemistry (AESEC), was used to probe the fate of elements during passivation of the Cantor high entropy alloys. Specially attention was paid on the effect of nitrogen addition and the dissolved oxygen on the elemental behavior. It was found that passivation of the Cantor alloys was a selective dissolution (incongruent dissolution) process with Cr primarily enriched on the surface. The addition of nitrogen improved the passivation proficiency by reducing the active dissolution prior to passivation. As a result, the Cantor-N alloy with added nitrogen was found to spontaneously passivate at the open circuit potential (Eoc) after the passive film was compromised. Spontaneous passivation involved surface enrichment of Cr as well as Mn to a lesser degree. It was posited that N bonded with Cr in the Cantor-N alloy formed the interstitial compound CrN that is highly resistant to dissolution and is capable of transforming to Cr oxide at the active potential.

Dissolved oxygen increased anodic dissolution during Eoc for Cantor alloy but improved the passivity for Cantor-N alloy. This phenomenon was explained using the elementally resolved polarization curve. Dissolved oxygen also improved the anodic passivation for both alloys. The specimens passivated at a constant anodic potential in the oxygenated electrolytes showed lower dissolution as compared to their counterparts passivated in aerated and deaerated solutions. Oxygen is therefore suggested to be a more efficient passivating agent as compared to water at sufficiently high anodic potential.