Imidazole- and mercaptobenzimidazole-derivatives as corrosion inhibitors for Cu, Cu–Zn alloys, and Zn in chloride solution

The electrochemical behaviour and surface conditions of Cu, Cu₇₀Zn₃₀ (at%), Cu₃₀Zn₇₀, and Zn in 3 wt% NaCl solution were investigated with and without the addition of 1 mM imidazole- and mercaptobenzimidazole-derivatives. In total, seven different inhibitor compounds were considered. Polarisation resistance and electrochemical impedance values at 0.01 Hz indicated that the corrosion inhibitor 2-mercapto-5-methoxybenzimidazole performed best on Cu and Cu₇₀Zn₃₀, whereas 5-amino-2-mercaptobenzimidazole was most effective for Zn and Cu₃₀Zn₇₀. The inhibitors significantly increased the polarisation resistance and impedance values for the studied metals and alloys, with Cu₇₀Zn₃₀ exhibiting an improvement of nearly two orders of magnitude. Potentiodynamic polarisation tests revealed that the inhibitors act as mixed-type inhibitors, primarily affecting anodic reactions. The XPS analysis demonstrated that the efficacy of these inhibitors is closely related to their functional groups: Cu, Cu₇₀Zn₃₀, Cu₃₀Zn₇₀, and Zn benefit from the mercapto group, while the amino group is particularly effective for Zn-rich alloys. DFT adsorption calculations, performed with an implicit aqueous solvent, revealed a strong adsorption affinity of both mercapto and amino groups toward Cu and Zn surfaces, with the amino group exhibiting a more notable interaction than the mercapto group on Zn—consistent with its experimentally observed inhibition effect.