Transpassive corrosion mechanisms in Ni revisited with electrochemistry coupled in situ respirometry

In this study, we investigate the transpassive corrosion mechanisms in Ni using in situ respirometry coupled with electrochemical experiments to decouple contributions from multiple anodic reactions occurring simultaneously. In the transpassive regime, the dissolution clearly starts prior to the onset of oxygen evolution reaction (OER) as confirmed with potentiodynamic and potentiostatic measurements. The onset of OER also coincides with formation of a secondary passive film, likely comprising of Ni (III) species, suppressing the dissolution. We show that acidification of the electrolyte occurs after the onset of OER, but it does not trigger the transpassive dissolution in Ni. Furthermore, the post-mortem characterization revealed a selective grain boundary attack. The findings are discussed considering existing literature concerning the interplay between OER, secondary passivation and dissolution in the transpassive regime.