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

Highlights: • 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. - Abstract: 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.