Chemical interaction between nitrogen-doped graphene defects and a copper (111) surface: Effects on water molecule adsorption

The electronic properties of nitrogen-doped graphene (pyridinic, pyrrolic and graphitic defects) supported by a copper substrate and their effects on water molecule adsorption have been studied by applying density functional theory, together with the vdW-DF correction. We discovered that pyrrolic and pyridinic defects strongly interact with the copper substrate due to covalent chemical bonds between the nitrogen atoms and the underlying metal. The binding energy and charge transfer from the copper to nitrogen atoms induces a formal oxidation state in the copper [copper (I) or copper (II)], depending on the type of defect which interacts. The effects of the metallic support on pyridinic, pyrrolic and graphitic defects influence the adsorption properties of water molecules. For nitrogen-doped graphene without substrate, the interaction of the water molecule with the pyridinic or pyrrolic defects consists mostly of hydrogen bonds and once a water molecule is adsorbed into a nitrogen site, this promotes the adsorption of the next molecule. Likewise, for the sheet bound to the copper substrate, an increase in van der Waals interactions for the water molecule adsorption occurs, due to the proximity between the sheet and the substrate.