Calcium-decorated graphyne nanotubes as promising hydrogen storage media: A first-principles study

First principles calculations based on density functional theory are carried out to study the hydrogen storage properties of Ca-decorated graphyne nanotubes. The results show that Ca atoms can be adsorbed stably on the acetylenic ring of the graphyne nanotube (GNT) without Ca atom clustering. Both the polar interactions and the orbital hybridizations contribute to the adsorption of H2 molecules. The average adsorption energy is in the range of 0.13–0.33 eV/H2 which is almost independent of the tube diameter. Each Ca atom can adsorb up to four H2 molecules due to the steric hindrance of the H2 molecules. With a hydrogen uptake of 7.44–8.96 wt%, the Ca-decorated GNT is an optimal choice for hydrogen recycling at near ambient conditions. - Graphical abstract: 2D contour of charge density of Ca decorated GNT2 and the side view of Ca decorated GNT2 with full loaded H2 molecules. Highlights: ► Ca decorated graphyne nanotubes as hydrogen storage media. ► The gravimetric density of H2 is 7.44–8.96 wt%. ► The average adsorption energy of hydrogen molecule is 0.13–0.33 eV/H2. ► It can operate under ambient thermodynamic conditions.