Li修饰的C_(24)团簇的储氢性能

Hydrogen storage properties of Li-decorated C_(24) clusters

利用密度泛函理论研究了Li原子修饰的C_(24)团簇的储氢性能.Li原子在C_(24)团簇表面的最佳结合位是五元环.Li原子与C_(24)团簇之间的作用强于Li原子之间的相互作用,能阻止它们在团簇表面发生聚集.当Li原子结合到C_(24)表面时,它们向C原子转移电子后带正电荷.当氢分子接近这些Li原子时,在电场作用下发生极化,通过静电相互作用吸附在Li原子周围.在Li修饰的C_(24)复合物中,每个Li原子能吸附两到三个氢分子,平均吸附能处于0.08到0.13 eV/H_2范围内.C_(24)Li_6能吸附12个氢分子,储氢密度达到6.8 wt%.

Hydrogen is considered as a potentially ideal substitution for fossil fuels in the future sustainable energy system because it is an abundant,clean and renewable energy carrier.A safe,efficient and economic storage method is the crucial prerequistite and the biggest challenge for the wide scale use of hydrogen.The nanomaterial is one of the most promising hydrogen storage materials because of its high surface to volume ratio,unique electronic structure and novel chemical and physical properties.It has been demonstrated that pristine nanostructures are not suitable for hydrogen storage,since they interact weakly with hydrogen molecule and their hydrogen storage density is very low.However,the hydrogen storage capacity of the nanostructures can be significantly enhanced through substitutional doping or decoration by metal atoms.Using density functional theory,we investigate the properties of hydrogen adsorption on Lidecorated C24 clusters.Results show that the preferred binding site for Li atom is the pentagonal rings.The interaction of Li atoms with the clusters is stronger than that among Li atoms,thus hindering effectively aggregation of Li atoms on the surface of the cluster.The decorated Li atoms are positively charged due to electron transfer from Li to C atoms.When H2 molecules approach Li atoms,they are moderately polarized under the electric field,and adsorbed around the Li atoms in molecular form.Each Li atom in the Li-decorated C24 complexes can adsorb two to three H2 molecules.The H–H bond lengths of the adsorbed H2 molecules are slightly stretched.The average adsorption energies are in the range of 0.08 to 0.13 eV/H2,which are intermediate between physisorption and chemisorption.C24 Li6 can hold up to12 H2 molecules,corresponding to a hydrogen uptake density of 6.8 wt%.This value exceeds the 2020 hydrogen storage target of 5.5 wt% proposed by the U.S.Department of Energy.