Potassium decorated γ-graphyne as hydrogen storage medium: Structural and electronic properties

Abstract

Different sites for K adsorption in γ-graphyne were investigated using density functional theory (DFT) calculations and optical and structural properties of the structures were examined. For the most stable structures, we put one H2 molecule in different directions on the various sites to evaluate the hydrogen adsorption capability of them. Then, one to nine H2 molecules in sequence were added to the best structure. Results show that clustering of the K atoms is hindered on the graphyne surface and the most desirable adsorption site for K atom is the hollow site of 12-membered ring with adsorption energy of 5.86 eV. Also, this site is the best site for H2 adsorption onto K-decorated graphyne with Edas of −0.212 eV. Adding of number of H2 molecule on this site shows that K atom can bind nine H2 molecules at one side of the graphyne with the average adsorption energy of 0.204 eV/H2. Therefore, for one side ca. 8.95 wt % and for both sides of the graphyne with a K atom in each side ca. 13.95 wt % of the hydrogen storage capacity can be achieved. This study shows that K-decorated graphyne can be a promising candidate for the hydrogen storage applications.