The topology impact on hydrogen storage capacity of Sc-decorated ever-increasing porous graphene.

Hydrogen storage capacity of different scandium (Sc)-decorated topological porous graphene (PG) was examined through density functional theory calculations. PGs were selected considering odd and even topological symmetries. Our calculations demonstrate that the most preferable sites for adsorption of Sc are located on the center of carbon rings on the perimeter of pores of all sizes. This results in stronger polarization and hybridization perpendicular to the surface leading to enhanced binding. Thus, all PGs are suitable for hydrogen storage under surrounded settings. Furthermore, results showed that the adsorption energies of H2 molecules increased gradually with the size of pores. Analysis of charge density difference showed that the presence of Sc could play an efficient role for stronger adsorption of hydrogen molecules rather than increasing pore sizes. Furthermore, projected densities of states indicate that favorable systems for hydrogen storage are those that have higher overlap of individual states at Fermi level. Compared with H2 adsorption on pure graphene, injecting topological defect such as hexagon porous and decoration with a transition metal atom such as Sc can effectively create much more conductive states at Fermi energy. Eventually, Sc decoration leads to n-type doping of PGs that help in much easier transportation of charge carriers and desirable storage of H2 molecules.