Investigation of the H2 dissociation and strengthening mechanism in vacancy-induced graphene

Abstract

Atomic vacancies play a crucial role in hydrogen storage and local strengthening of a substance with a mechanism that is elusive. First-principles examinations of monolayer graphene unveiled the following: (i) the neighboring carbon atoms move radially away from the vacancy center with a 3–10% C–C bond contraction, generating a circumferential density ribbon of energy and electrons; (ii) the dense electrons within the ribbon polarize the edge atoms into dipoles pointing to the center; (iii) the polarized electrons coupled together to for the vacancy dipole, resulting in the Dirac-Fermion resonant peak at Fermi energy and the energy density gai raise the local strength; and (iv) the vacancy dipole induces the adsorbed H2 molecule into H+-H- dipole to stabilize H2 adsorption. The findings of vacancy reinforcement, dipole formation, and stable H2 adsorption should provide a promising mechanism contributing to the advancement of hydrogen storage theory.