Reinforcing the tetracene-based two-dimensional C₄₈H₁₆ sheet by decorating the Li, Na, and K atoms for hydrogen...

To meet the increasing need of energy resources, hydrogen (H₂) 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 H₂ 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 H₂ 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 H₂ adsorption energy than the H₂ 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-σ orbital to s orbital of alkali metal atoms on the C₄₈H₁₆ sheet, leads to the enhancement of H₂ binding. Compared to H₂ adsorption on Na and K atom decorated C₄₈H₁₆ sheet, the H₂ 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 H₂ 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 H₂ storage.