Insights into the mechanism of electric field regulating hydrogen adsorption on Li-functionalized N-doped defective graphene: A first-principles perspective

The hydrogen storage properties of lithium functionalized graphene under external electric fields have been studied in this work employing density functional theory (DFT) calculations. Lithium modified nitrogen doped double-vacancy graphene (Li_NDVG) was constructed as hydrogen storage material. It is examined in terms of the system's electronic properties, H2 adsorption energy, and stable configuration. The results demonstrate that Li atoms can be distributed on the substrate surface and incorporated into defect centers without producing metal clusters. In comparison to pristine graphene, the adsorption energy of H2 on Li_NDVG is four times higher. The Coulomb force between Li atom and H2 molecule grows as the positive electric field's strength increases, and the adsorption distance shrinks. On the contrary, the H2 adsorption energy decreases as the negative electric field's strength increases, and the adsorption distance expands. Furthermore, adsorption occurs spontaneously within the range of 0-300 K and 1-100 atm, and the promoting effect of a positive electric field on adsorption only occurs in the temperature range of 0-140 K. Hydrogen storage properties of functionalized graphene modified with lithium trimer and tetramer respond to the electric field in the same way as single atom. And the presence of clusters and positive electric field increases the bond length of the H2 molecule, causing a tendency for the H2 molecule to dissociate.