Reinforcing the tetracene-based two-dimensional CH 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) 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 (CH) is investigated for H storage using the density functional theory. To explore the hydrogen storage capacity, the hydrogen molecule is initially positioned parallel to the CH 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 adsorption on the CH sheet. The Li atom decorated CH sheet has a higher binding energy value of -2.070 eV than the Na and K atom decorated CH sheet. The presence of Li, Na, and K atoms on the CH sheet enhance the H adsorption energy than the H on the pristine CH sheet. The decrease of Mulliken charge in alkali metal atoms (Li, Na, and K atom) on the CH sheet reveal that the electron is transferred from H-σ orbital to s orbital of alkali metal atoms on the CH sheet, leads to the enhancement of H binding. Compared to H adsorption on Na and K atom decorated CH sheet, the H adsorption on Li atom decorated CH sheet has the maximum adsorption energy value of -0.389 eV. The obtained hydrogen storage capacity of Li, Na, and K atoms decorated CH sheets are about 7.49 wt%, 7.31 wt%, and 7.14 wt% respectively for four H 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 CH sheets with Li, Na, and K atom plays the potential role in the H storage.