碳硼富勒烯衍生物C18B2M（M=Li，Ti，Fe）的储氢性能计算研究∗

摘要

The generalized gradient approximation of density functional theory is applied to study the hydrogen storage capacity of the alkali metal atom Li, transition metal atoms Ti and Fe decorated C18B2M (M =Li, Ti, Fe) fullerenes. It is found that the metal is bonding to C18B2 stronger than to C20. When the average adsorption energy of C18B2Li-nH2 is low, and the binding of H2 to C18B2Fe is too strong, C18B2Ti-nH2 has the average adsorption energy between 0.45—0.59 eV, which is in the range from 0.2 to 0.6 eV, so it can realize the reversible adsorption of H2. A maximum number of H2 adsorbed on to C20B2M (M =Li, Ti, Fe) should be 4, 6, and 4, for Li, Ti, and Fe respectively;this agrees well with the 18 electronic rule. C18B2Li adsorbs H2 molecules mainly through the static electronic field formed by Li ions, while C18B2Ti and C18B2Fe adsorb H2 mainly through the Kubas interaction. Therefore, C18B2Ti can not only adsorb more H2 molecules, but also realize the reversible hydrogen storage.%本文使用密度泛函理论(density functional theory, DFT)中的广义梯度近似(generalized gradient ap-proximation, GGA)研究了经碱金属原子Li、过渡金属原子Ti和Fe原子修饰的富勒烯C18B2M (M =Li, Ti, Fe)的储氢性能.研究发现, C18B2由于B的替代掺杂,比C20对金属原子具有更高的结合能.由平均吸附能分析可知： C18B2Li对H2的吸附能力较弱, C18B2Fe对H2的吸附能力过强,而C18B2Ti对H2的平均吸附能介于0.45—0.59 eV 之间,介于物理吸附和化学吸附之间(0.2—0.6 eV),因此可以实现常温下的可逆储氢. C18B2M (M =Li, Ti, Fe)能够吸附的H2数目最多分别为4,6和4.由储氢机理分析可知： C18B2Li主要通过碱金属离子激发的静电场来吸附H2,而C18B2Ti和C18B2Fe主要通过金属原子与H2之间的Kubas作用来吸附H2.由于C18B2Ti既有较大的储氢数目,又可以实现可逆储氢,因此有望开发成新型纳米储氢材料.