Corrosion inhibition of carbon-steel with 2-mercaptobenzimidazole in hydrochloric acid

• Inhibition efficiency of 2-mercaptobenzimidazole is similar in 0.01–1 M HCl.
• 2-mercaptobenzimidazole acts as mixed inhibitor in 0.1 M and 1 M HCl.
• Inhibition evolves to be predominantly anodic in nature in 0.01 M HCl.
• Cathodic O2 reduction is less well impeded by 2-mercaptobenzimidazole.
• XPS indicates that the interface varies with both HCl and MBI concentration.

Electrochemical measurements and substrate analysis have been employed to probe the corrosion inhibition performance of 2-mercaptobenzimidazole (MBI) for carbon-steel in 1 M, 0.1 M, and 0.01 M HCl. Data demonstrate that the inhibition efficiency of MBI is essentially independent of HCl concentration. Moreover, it is concluded that the presence of MBI impedes the cathodic reduction of dissolved O2 to a lesser extent than H+. X-ray photoelectron spectra indicate that substrate termination varies as a function of both HCl and MBI concentration, with the interface consisting of MBI bound to film-free carbon-steel on highly inhibited substrates.