关键词: 石墨烯, Sc, 电子性质, 储氢, 密度泛函理论

With the extensive use of fossil fuels such as coal and oil, the energy crisis and the accompanying environmental pollution has become a serious problem today, hydrogen has attracted widespread concern because of its less pollution and renewable usage. One of the key issues affecting the widespread use of hydrogen energy is the hydrogen storage. The metal decorated nanomaterials exhibited remarkable hydrogen adsorption capacities. The generalized gradient approximation based on density functional theory is used to study the geometric structure, electronic property, and hydrogen storage capacity of the Sc atom decorated expanded sandwich type structure graphene-Sc₂-graphene. It is calculated that the structure with the Sc atom locating above the hollow site of the hexagonal ring on the graphene plane has the largest binging energy, but smaller than the experimental cohesive energy of bulk Sc (3.90 eV). However, when one or more Sc atoms locate between two graphene layers and about 2 Å distance to the substrate, the binding energy of the Sc atom to the substrate increase up to 5 eV, much larger than the experimental cohesive energy of bulk Sc (3.90 eV), so can prevent them from clustering on the graphene surface. Therefore, the sandwich type structure obviously increases the binding strength between the Sc atom and the substrate. It is known from the 18-electron rule that the structure can be stabilized through adsorbing the hydrogen molecules. Therefore, they can become the ideal hydrogen storage nanomaterials. Each Sc in the graphene-Sc-graphene sandwich type structure can adsorb up to two H₂ molecules, and the average adsorption energy of H₂ for graphene-(Sc-H₂)-graphene and graphene-(Sc-2H₂)-graphene are 0.67 eV and 0.54 eV respectively, which are between the physical adsorption and chemical adsorption (0.1～0.8 eV), therefore, they can realize the reversible adsorption of hydrogen. The expanded graphene-Sc-graphene sandwich type structure adsorbs hydrogen mainly through the Dewar-Kubas interaction and forms the π-δ-π electronic structure.

Key words: graphene, Sc, electronic property, hydrogen storage, density functional theory