Density Functional Theory Study of Superalkali NLi4-Decorated Graphdiyne Nanosheets as Hydrogen Storage Materials

The properties and mechanism of adsorption of hydrogen molecules on NLi4-decorated graphdiyne nanosheets (NLi4-GDY) were investigated based on the density functional theory. Accordingly, the 76 hydrogen storage configurations of NLi4-SGDY, NLi4-GDY-A, and NLi4-SGDY-A were constructed by nonmetallic B/N substitution and A (A = B, N, Si, P) adsorption. The electronic structure of each configuration and the structure with the desired high hydrogen storage capacity were explored. The results showed that the charge on the lithium atom in the NLi4-GDY structure was transferred to the pristine GDY, thus forming a partial electron field around each lithium atom, which subsequently led to the polarized adsorption of the hydrogen molecule. Through B/N substitution and A adsorption, we have modulated the degree of charge transfer in Li atoms across different configurations, thereby manipulating the strength of partial electric fields and resulting in varying hydrogen storage capacities for NLi4-SGDY, NLi4-GDY-A, and NLi4-SGDY-A configurations. According to DFT calculations, the optimal hydrogen storage structures for NLi4-GDY, NLi4-SGDY, NLi4-GDY-A, and NLi4-SGDY-A were 6H2-2NLi4-GDY, 14H2-2NLi4-N11′, 14H2-2NLi4-GDY-Si, and 18H2-2NLi4-N1-P, respectively, with gravimetric densities of 3.85, 8.09, 7.29, and 8.91 wt %, respectively. Considering the exceptional hydrogen storage properties of the aforementioned configurations, we propose that NLi4-decorated GDY with B/N substitution and A adsorption offers a promising avenue for discovering novel hydrogen storage materials.