各Li吸附组分下硅烯氢存储性能的第一性原理研究

First-principles study of hydrogen storage properties of silicene under different Li adsorption components

利用Li原子对硅烯进行表面修饰是提高硅烯氢存储能力的一种有效方法.为了充分挖掘Li修饰硅烯的氢存储性能,本文采用范德瓦耳斯作用修正的第一性原理计算方法,对不同Li吸附组分下硅烯的结构、稳定性和氢存储能力进行了研究.研究结果表明,硅烯体系能够在Li组分从0.11增加到0.50时保持稳定,其最大储氢量随Li组分的增加而增大,氢气平均吸附能则存在减小趋势;当Li组分达到0.50而饱和时,硅烯体系具有最大的储氢量,相应的质量储氢密度为11.46 wt%,平均吸附能为0.34 eV/H2,远高于美国能源部设定的储氢标准,表明提高Li组分甚至使其达到饱和在理论上能有效提高Li修饰硅烯的储氢性能.此外,通过对Mulliken电荷布居、差分电荷密度和态密度的分析,发现Li修饰硅烯的储氢机制与电荷转移诱导的静电相互作用和轨道杂化作用有关.研究结果可为Li修饰硅烯在未来氢存储领域的应用提供理论指导.

Alkali metal has predicted to be a promising candidate for decorating silicene surface to obtain the high hydrogen storage capacity, owing to their physical properties of lightweight, lower cohesive energy, and appropriate strength of the interaction with H_2 molecules. However, though the high potential in hydrogen storage of alkali metal adatoms-decorated silicene under the fixed adatom adsorption component is well known, the evidence for the hydrogen storage capacity of alkali metal adatoms-decorated silicene under different adatom adsorption components remains largely unexplored,which may be of great significance to make the most advantages of alkali metal adatoms-decorated silicene in hydrogen storage aspects. Herein, according to the first-principles calculation corrected by the van der Waals effect, we take Lidecorated silicene for example and perform the detailed study of the geometry structure, the stability and the hydrogen storage capacity of silicene under different Li adsorption components（LixSi1-x）, aiming to maximize the hydrogen storage performance of Li-decorated silicene. The results show that the preferred site of Li changes from the hollow site to the valley site as the Li component increases from 0.11 to 0.50, and binding energy of Li is always greater than the corresponding cohesive energy, showing the high stability of Li-decorated silicene and the feasibility of the method to obtain a higher hydrogen storage capacity by increasing the Li component. The hydrogen storage of silicene under different Li adsorption components is investigated by the sequential addition of H2 molecules nearby Li atoms in a stepwise manner. It can be observed that the hydrogen storage capacity of Li-decorated silicene increases and the average adsorption energy decreases with the increase of the Li component. The corresponding hydrogen storage capacities of Li0.11Si0.89, Li0.20Si0.80, Li0.33Si0.67, Li0.43Si0.57 can reach up to 2.54 wt%, 4.82 wt%, 6.00 wt% and 9.58 wt% with0.58 eV/H2, 0.47 eV/H2, 0.54 eV/H2 and 0.41 eV/H2 average adsorption energy, respectively. When the Li component increases up to 0.50, Li atoms are saturated with a maximum hydrogen storage capacity of 11.46 wt% and an average adsorption energy of 0.34 eV/H2, which well meet the hydrogen storage standard set by the U.S. Department of Energy and mean that the hydrogen storage can be theoretically improved by increasing the Li adsorption component to a saturated level. Furthermore, we analyze the Mulliken charge population, the charge density difference and the density of states, showing that the charge-induced electrostatic interaction and the orbital hybridization are the key factors for the hydrogen adsorption of Li-decorated silicene. Our results may enhance our fundamental understanding of the hydrogen storage mechanism and explore the applications in areas of hydrogen storage for Li-decorated silicene, which are of great importance for the usage of hydrogen in the future.