Reinforcing the tetracene-based two-dimensional C48H16 sheet by decorating the Li, Na, and K atoms for hydrogen storage and environmental application -A DFT study

To meet the increasing need of energy resources, hydrogen (H-2) is being considered as a promising candidate for energy carrier that has motivated research into appropriate storage materials among scientists. Thus, in this study for the first time, zig-zag and armchair edged tetracene based porous carbon sheet (C48H16) is investigated for H-2 storage using the density functional theory. To explore the hydrogen storage capacity, the hydrogen molecule is initially positioned parallel to the C48H16 sheet at three different sites, resulting in lower adsorption energies of -0.020, -0.024, and -0.015 eV respectively. The Li, Na, and K atoms are decorated to improve H-2 adsorption on the C48H16 sheet. The Li atom decorated C48H16 sheet has a higher binding energy value of 2.070 eV than the Na and K atom decorated C48H16 sheet. The presence of Li, Na, and K atoms on the C48H16 sheet enhance the H-2 adsorption energy than the H-2 on the pristine C48H16 sheet. The decrease of Mulliken charge in alkali metal atoms (Li, Na, and K atom) on the C48H16 sheet reveal that the electron is transferred from H- s orbital to s orbital of alkali metal atoms on the C48H16 sheet, leads to the enhancement of H2 binding. Compared to H-2 adsorption on Na and K atom decorated C48H16 sheet, the H-2 adsorption on Li atom decorated C48H16 sheet has the maximum adsorption energy value of 0.389 eV. The obtained hydrogen storage capacity of Li, Na, and K atoms decorated C48H16 sheets are about 7.49 wt%, 7.31 wt%, and 7.14 wt% respectively for four H-2 molecules, which is greater than the targeted hydrogen storage capacity of the United States Department of Energy (DOE). Thus the obtained results in this work reveal that the decorated C48H16 sheets with Li, Na, and K atom plays the potential role in the H-2 storage.