I work in the field of brass corrosion (Cooper and Zinc) in a 3 ′ / • NaCl medium. At the anodic part of the polarization curve, we notice a gas evolution on the counter-electrode (platinum) and a small passivation around + 100mV followed by a re-increase of the current. the overvoltage range is -700mV at Ecor = -220mV and Ecor up to + 200mV. At the end of experiment there is a blue precipitation and the pH is around 8,5.
My question is: What are responsibles of the release of gas and the passivation.
Many thanks.