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

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 (300 K) 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.