Li decorated C9N4 monolayer as a potential material for hydrogen storage

Based on first−principles calculations, we investigate the possibility of the two-dimensional porous C9N4 material as for hydrogen storage, and find that the adsorption energy of H2 molecules on the pristine C9N4 is too weak to meet the requirements of hydrogen storage, whereas the adsorption on the Li−decorated sheet is relatively moderate. Each C9N4 unit cell can incorporate 6 Li atoms, of which 3 Li atoms are located above the intrinsic hole and the others are below. The unit cell can hold 14 hydrogen molecules with an average adsorption energy of −0.12 eV, which meets the reversible storage condition of hydrogen, and the gravity density reaches 7.04 wt%. Particularly, 6Li@C9N4 maintains excellent H2 storage performance under a tensile strain within 2%. The ab initio MD simulations performed at 300 K show that all 14 H2 molecules remained on the double sides of 6Li@C9N4 in the absence and presence of strain. Therefore, we predict that Li−modified C9N4 could be a potential material with excellent ductility for hydrogen storage at room temperature.