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

Different sites for K adsorption in gamma-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 H-2 molecule in different directions on the various sites to evaluate the hydrogen adsorption capability of them. Then, one to nine H-2 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 H-2 adsorption onto K-decorated graphyne with E-das of -0.212 eV. Adding of number of H-2 molecule on this site shows that K atom can bind nine H-2 molecules at one side of the graphyne with the average adsorption energy of 0.204 eV/H-2. 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. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.