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Abstract

In real environments, copper and other metal surfaces are never clean. Even during active
dissolution in corrosion, they are likely to be covered with adsorbed corrosion-relevant
species such as O, OH, H, and Cl. To explore the impact of such species on the bonding
of imidazole, used herein as an archetypal model of azole corrosion inhibitors on Cu(111),
we conducted a systematic computational study based on the Density-Functional Theory.
Over 400 diverse adsorption configurations were considered, with close attention paid to
the effects of variables such as surface coverage, the type of corrosion-relevant species,
and the distance between the imidazole molecule and the corrosion-relevant species. We
demonstrate that O and Cl enhance the adsorption bonding of imidazole, while H has
almost no effect, and OH either diminishes or has a negligible impact on the imidazole adsorption.
The effect of the adsorbed corrosion-relevant species on the imidazole adsorption
usually diminishes with the increasing distance between adsorbed species and imidazole,
and with decreasing coverage of corrosion-relevant species. We identified three coadsorption
effects of O, OH, H, and Cl on the non-dissociative adsorption of imidazole, including
hydrogen bond formation, enhancement of the N–Cu bond, and work-function change induced
by coadsorbates. We also found that if the coverage of corrosion-relevant species is
too high, then the chemisorption of imidazole is prevented either sterically or due to the
unavailability of free surface sites.
Moreover, our study shows that chemisorbed O and OH species promote deprotonation
of azole molecules on the investigated copper surfaces, as exemplified by benzotriazole,
imidazole, and Cu(111). The N–H bond cleavage is involved in such deprotonation. By
undergoing molecular deprotonation during adsorption, the resulting adsorption states are
more stable, which increases the persistence of chemisorbed azole molecules. Our findings
demonstrate that deprotonated benzotriazole molecules exhibit stability that is roughly
1 eV higher on O/Cu(111) and OH/Cu(111), compared to an adsorbed intact molecule on
bare Cu(111). However, for imidazole, the degree of stabilization is significantly weaker
and ranges from 0.1 to 0.5 eV.
Further, we investigated the formation of coordination complexes between copper central
ions and 19 different N-heterocyclic inhibitor molecules in an aqueous medium, using a
cluster/continuum model, which involves a few explicit water molecules and the surrounding
water described implicitly. Our results indicate that most of the investigated ligands
have the potential to coordinate with Cu(I) and Cu(II) ions, forming stable two- or fourcoordinated
complexes, respectively. The thermodynamic stability of these coordination
compounds was also evaluated.