内掺Sc原子的扩展三明治结构graphene-Sc-graphene的几何结构,电子性质和储氢性能研究

Geometric Structure, Electronic Property, and Hydrogen Storage Capacity of the Sc Atoms Decorated Expanded Sandwich Type Structure Graphene-Sc-graphene

使用密度泛函理论中的广义梯度近似对内掺Sc原子的graphene-Sc-graphene扩展三明治结构的几何结构、电子结构和储氢性能进行计算研究.计算发现：Sc原子位于单层石墨烯中六元环上方的结构具有较大的结合能,但小于固体Sc的内聚能实验值（3.90eV）,然而,当单个Sc原子或者多个Sc原子在双层石墨烯中间与底层相距2？时,Sc原子与基底的结合能增加到5eV以上,远远大于固体Sc的内聚能实验值（3.90eV）,因此相邻的Sc原子可以有效避免成簇.由此可见,三明治结构的形成明显增加了Sc原子与基底的结合强度,该结构可以进一步储氢来满足18电子规则而更加稳定,从而成为理想的新型储氢纳米材料.扩展三明治结构graphene-Sc-graphene的（2×3）单元中每个Sc原子最多可以吸附2个H_2分子,对H_2的平均吸附能分别为0.67eV和0.54eV,介于物理吸附和化学吸附（0.1~0.8eV）之间,因此该体系可以实现常温常压下对H_2的可逆吸附.由储氢机制分析可知：扩展三明治结构graphene-Sc-graphene主要通过Dewar-Kubas作用进行储氢,形成了π-δ-π型的电子结构.

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 e V）. However, when one or more Sc atoms locate between two graphene layers and about 2 ？ distance to the substrate, the binding energy of the Sc atom to the substrate increase up to 5 e V, much larger than the experimental cohesive energy of bulk Sc（3.90 e V）, 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 H_2 molecules, and the average adsorption energy of H_2 for graphene-（Sc-H_2）-graphene and graphene-（Sc-2H_2）-graphene are 0.67 e V and 0.54 e V respectively, which are between the physical adsorption and chemical adsorption（0.1 ~ 0.8 e V）, 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.