DFT Study of Azole Corrosion Inhibitors on Cu2O Model of Oxidized Copper Surfaces: II. Lateral Interactions and Thermodynamic Stability

The adsorption of imidazole, triazole, and tetrazole-used as simple models of azole corrosion inhibitors-on various Cu2O(111)- and Cu2O(110)-type surfaces was characterized using density functional theory (DFT) calculations with the focus on lateral intermolecular interactions and the thermodynamic stability of various adsorption structures. To this end, an ab initio thermodynamics approach was used to construct two-dimensional phase diagrams for all three molecules. The impact of van der Waals dispersion interactions on molecular adsorption bonding was also addressed. Lateral intermolecular interactions were found to be the most repulsive for imidazole and the least for tetrazole, for which they are usually even slightly attractive. Both non-dissociative and dissociative adsorption modes were considered and although dissociated molecules bind to surfaces more strongly, none of the considered structures that involve dissociated molecules appear on the phase diagrams. Our results show that the three azole molecules display a strong tendency to preferentially adsorb at reactive coordinatively unsaturated (CUS) Cu surface sites and stabilize them. According to the calculated phase diagrams for Cu2O(111)-type surfaces, the three azole molecules adsorb to specific CUS sites, designated as Cu-CUS, under all conditions at which molecular adsorption is stable. This tentatively suggests that their corrosion inhibition capability may stem, at least in part, from their ability to passivate reactive surface sites. We further comment on a specific drawback due to neglect of configurational entropy that is usually utilized within the ab initio thermodynamics approach. We analyze the issue for Langmuir and Frumkin adsorption models and show that when configurational entropy is neglected, the ab initio thermodynamics approach is too hasty to predict phase-transition like behavior.