Li-decoration on the edge oxidized graphyne and graphdiyne: A first principles study

In recent years, the new two-dimensional planar carbon allotropes, graphyne and graphdiyne, have received significant research attention. Accordingly, the present study is devoted to investigate how the electronic structures of graphyne and graphdiyne nanoflakes are modified upon the edge oxidizing as well as Li-decoration. Different oxygen containing groups such as carbonyl, ketone, hydroxyl, carboxylic, formyl, and epoxide are considered for oxygenation of these carbon surfaces. The stability of oxidized surfaces with respect to the bare sheets has been discussed in terms of Gibbs free energy of formation. We showed that carbon surfaces terminated with carboxylic group are more stable than other oxidized surfaces. It is also found that the band gap in considered surfaces can be tuned (0.53-1.51 eV) by changing the type of oxygen containing group. Moreover, we report the binding energies for the Li adsorption at hollow sites on the basal plane and on the oxygen of functional group. Our calculations reveal that the interaction between oxygen group and carbon atoms at the edge increases the reactivity of considered sheets toward Li adsorption. The band gap of fuctionalized surfaces can be engineered by selective lithiation over a wide range between 0.01 and 1.31 eV. We found that the oxygen species plays the key role on the Li adsorption on the edge oxidized surfaces leading to either semiconducting or metallic behaviors. However, this study offers critical information for further theoretical and experimental studies on oxidized carbon materials for their possible applications in lithium ion batteries as well as hydrogen storage materials. (C) 2016 Elsevier B.V. All rights reserved.