Toward Tunable CO Adsorption on Defected Graphene: The Chemical Role of Ni(111) and Cu(111) Substrates

Fine-tuning the electronic and chemical properties of graphene is currently one of the main goals in chemical physics. While pristine graphene is chemically inert, point-like defects such as small vacancies or substitutional atoms can substantially alter the local chemical environment, modifying graphene reactivity upon gas adsorption. Here we investigate from first-principles the effect of Cu(111) and Ni(111) substrates on graphene mono- and divacancies, revealing that transition-metal substrates can significantly contribute to both nonlocal dispersion forces and to the local reactivity. Nonsaturated carbons can strongly interact with the underlying metal atom, which-despite the substantial interlayer distance-protrudes from the (111) plane, binding to the vacancy. This mechanism can hinder chemical adsorption, with an effect that crucially depends on the actual metal substrate. We also find extremely low activation barriers for CO chemisorption on Ni(111)-supported graphene with divacancies, which we compare to recent experimental observations. The nontrivial role of transition metal substrates evidenced in our work suggests new pathways for fine-tuning the chemical properties of small vacancies, favoring many possible applications from defect healing and gas sensing to surface catalysis.