First principles studies of the interactions between alkali metal elements and oxygen-passivated nanopores in graphene

We characterize the structure-property relationship of alkali metal elements in oxygen-passivated graphene pores using the density functional theory that accounts for quantum mechanical effects and charge transfer. Our description is based on the structural and electronic properties of the system and shows common trends among the different alkali metals and pores. We find that these nanopores which serve as docking sites for alkali metal elements give the strongest binding when the size of the pore is similar to the element's van der Waals radius. A linear correlation between the binding energy and the energy location of the alkali element valence state is found for all elements and pores. Analysis of the charge transfer reveals that alkali adsorption increases the local charge in the perimeters of the pore by amounts that depend on the geometry. Moreover, charge distributions in pristine graphene resemble those of an ideal conductor despite its semimetallic character and atomic thickness while oscillations in the vicinity of O-passivated nanopores are observed. Our results suggest that charge transfer is localized within a few nanometers of the pore and, therefore, allude to high density energy storage. The outcomes of this work are significant towards the application of porous graphene as effective membranes for ion filtration of water and electrode applications.