Inhibiting properties of benzimidazole films for Cu(II)/Cu(I) reduction in chloride media studied by RDE and EQCN techniques

The effects of benzimidazole (BIM) and 2-methylbenzimidazole (MBIM) on the electroreduction of Cu(II) on a rotating Pt disk electrode in chloride media were investigated. These studies were undertaken in conjunction with earlier observation that these imidazole derivatives act as inhibitors of copper corrosion processes and are non-toxic. We have found that BIM and MBIM also form adsorption films on Pt which are able to inhibit one-electron reduction of Cu(II) to Cu(I) and prevent the development of convective diffusion limiting current wave. The inhibition was found to be controlled by electric field-assisted mass transfer through the film. The ingress of Cu(II) species into the film was detected using the EQCN technique. The EQCN measurements indicate that small fraction of Cu(I) formed in the film by reduction of Cu(II) is retained in the film, most likely in the form of CuCl. The amount of CuCl retained in strongly inhibiting films (e.g., at lower pH) is diminished. The inhibition effectiveness of Cu(II) reduction process by Pt–BIM and Pt–MBIM films increases strongly with increasing acidity of the medium in the pH range from 3 to 1. The mechanism of this remarkable pH effect has been proposed. The orientation of inhibitor molecules on an electrode surface has been evaluated using quantum mechanical calculations for a BIM molecule physisorbed on a model Pt18 atom cluster.