SECM study of the pH distribution over Cu samples treated with 2-mercaptobenzothiazole in NaCl solution

This paper reports the effect of treatment with 2-mercaptobenzothiazole (2MBT) (a corrosion inhibitor) on pH distribution over Cu samples monitored in situ using scanning electrochemical microscopy (SECM) in potentiometric mode. Line scans were conducted over two copper wires embedded in insulating resin, one of which had been pre-treated with 2MBT. It was found that the treated Cu sample had a less acidic character than the non-treated sample. Furthermore, the pH above the resin areas is considerably more acidic than that above either Cu wire. This feature is attributed to the consumption of OH- ions on the non-treated Cu wire during the formation of atacamite as a corrosion product, and the tautomeric equilibrium established by the detached 2-mercaptobenzothiazole molecules in the bulk electrolyte. These pH distributions are spatially resolved in the SECM mapping above both Cu wires.