First-principles study of hydrogen storage properties of Irida-graphene

Abstract

The hydrogen storage properties of the 2D carbon allotrope Irida-graphene (IG) were investigated using first-principles calculation. The intrinsic IG adsorption energy for H2 is only -0.06 eV, significantly lower than the effective adsorption threshold. To improve its hydrogen storage capabilities, IG was doped with boron (B) and modified with sodium (Na). It was found that both 2Na@IG and 2Na@BIG systems could adsorb 8 pairs of H2. However, the average adsorption energy of H2 in the 2Na@BIG system (-0.145 eV) is higher compared to that in the 2Na@IG system (-0.134 eV), and the adsorption capacity (14.6 wt.%) was superior to that of the 2Na@IG system (14.5 wt.%). The introduction of B created an electron-deficient structure (BIG), enhancing electron transfer between Na and the substrate to improve Na binding energy. This enhancement resulted in stronger polarization and orbital hybridization of H2 within the 2Na@BIG system compared to the 2Na@IG system, further boosting its adsorption performance. The charge transfer between Na and the substrate generated an electric field that polarized H2 adsorbed around Na, while the electric field generated by the already polarized H2 further polarizes the H2 adsorbed in the outer layer. Density of States(DOS) diagrams illustrated orbital hybridization of the H2 in both systems. Molecular dynamics simulations conducted at room temperature(300K) demonstrated that the 2Na@BIG system achieved a hydrogen storage capacity of 8.8 wt.%. In conclusion, both 2Na@IG and 2Na@BIG systems exhibit potential as H2 storage materials, but the 2Na@BIG system displays superior hydrogen storage performance compared to the 2Na@IG system.