Synergistic effect of 2-mercaptobenzimidazole and octylphosphonic acid as corrosion inhibitors for copper and aluminium – An electrochemical, XPS, FTIR and DFT study

Highlights: • Mercaptobenzimidazole (MBI) is a strong inhibitor of Cu corrosion. • Octylphosphonic acid (OPA) is a strong inhibitor of Al corrosion. • Synergistic effect was observed for formulation MBI:OPA = 90:10 on Cu but not on Al. • Synerigistically formed Cu(I)MBI polymer-like multilayer presents excellent barrier to corrosion. • pH plays a critical role in the formation of appropriate combination of stable metal species and inhibitor form. Inhibitory action of 2-mercaptobenzimidazole (MBI) and octylphosphonic acid (OPA) and their binary combinations on copper and aluminium in 3 wt.% NaCl was investigated by electrochemical methods, whereas the bonding of inhibitors was scrutinized by XPS and FTIR spectroscopies, wettability measurements, and DFT calculations. MBI is a good inhibitor for Cu but not for Al, whereas OPA behaves complementary. Although OPA is not an inhibitor for Cu, it can synergistically boost corrosion inhibition of copper when added to MBI. Evidence suggests that OPA changes the bonding of MBI by making the copper surface more susceptible to MBI resulting in a thicker and more protective organic film.