First-principles study of Li-doped planar g-C3N5 as reversible H2 storage material.

Under the background of energy crisis, hydrogen owns the advantage of high combustion and shows considerable environment friendliness; however, to fully utilize this novel resource, the major hurdle lies in its delivery and storage. The development of the in-depth yet systematical methodology for two-dimensional (2D) storage media evaluation still remains to be challenging for computational scientists. In this study, we tried our proposed evaluation protocol on a 2D material, g-C3N5, and its hydrogen storage performance was characterized; and with addition of Li atoms, the changes of its electronical and structural properties were detected. First-principles simulations were conducted to verify its thermodynamics stability; and, its hydrogen adsorption capacity was investigated qualitatively. We found that the charges of the added Li atoms were transferred to the adjacent nitrogen atoms from g-C3N5, with the formation of chemical interactions. Thus, the isolated metallic sites tend to show considerable electropositivity, and can easily polarize the adsorbed hydrogen molecules, and the electrostatic interactions can be enhanced correspondingly. The maximum storage capacity of each primitive cell can be as high as 20 hydrogen molecules with a gravimetric capacity of 8.65 wt%, which surpasses the 5.5 wt% target set by the U.S. Department of Energy. The average adsorption energy is ranged from -0.22 to -0.13 eV. We conclude that the complex 2D material, Li-decorated g-C3N5 (Li@C3N5), can serve as a promising media for hydrogen storage. This methodology provided in this study is fundamental yet instructive for future 2D hydrogen storage materials development.

Li-Decorated ß12-Borophene as Potential Candidates for Hydrogen Storage: A First-Principle Study.

The hydrogen storage properties of pristine ß12-borophene and Li-decorated ß12-borophene are systemically investigated by means of first-principles calculations based on density functional theory. The adsorption sites, adsorption energies, electronic structures, and hydrogen storage performance of pristine ß12-borophene/H2 and Li-ß12-borophene/H2 systems are discussed in detail. The results show that H2 is dissociated into Two H atoms that are then chemisorbed on ß12-borophene via strong covalent bonds. Then, we use Li atom to improve the hydrogen storage performance and modify the hydrogen storage capacity of ß12-borophene. Our numerical calculation shows that Li-ß12-borophene system can adsorb up to 7 H2 molecules; while 2Li-ß12-borophene system can adsorb up to 14 H2 molecules and the hydrogen storage capacity up to 10.85 wt %.