金属修饰共价有机骨架COF-1储氢性能的第一性原理研究

【作者】 赵慧；

【导师】 闫翠霞；

【作者基本信息】 昆明理工大学 ， 材料物理与化学， 2020， 硕士

【摘要】 氢能源由于自身所具有的无污染、储量丰富、储能密度大等特点被认为是21世纪理想的可以替代传统化石燃料的可再生清洁能源。氢能源的储存是决定氢能源能否快速发展的关键。近些年来,对于储氢的研究主要集中于氢燃料电池汽车上,但车载储氢依旧是一个难题。COF-1是一种二维的COF结构,在二维COF中具有最高的吸附焓,且在低温高压下表现出较好的储氢性能,但由于分子与COF-1之间是范德瓦尔斯相互作用,所以在室温下COF-1的储氢性能很差。研究表明,金属原子的掺杂能明显提高基底与氢分子的相互作用。基于上述背景,本文利用第一性原理,对金属修饰COF-1的储氢性能进行了研究。通过研究Li的修饰COF-1的储氢性能,发现Li原子在COF-1上的最优吸附位点是C六元环的中心位置,Li与COF-1的结合能为1.765 e V。这使得Li原子能稳定地吸附在上面,每个Li原子能稳定吸附3个H₂分子。当COF-1上Li原子覆盖浓度最大时,即6个Li吸附COF-1原胞上,此时每个Li原子能吸附3个H₂分子,所以6Li-COF-1能吸附18个H₂分子,储氢量为7.69 wt%。氢分子在Li-COF-1上的吸附主要是通过带电的Li原子与被极化的H₂分子之间的极化作用。从头算分子动力学结果表明,在300 K温度下,6个Li原子修饰的COF-1最多能吸附12个H₂氢分子,储氢量为5.26 wt%。对Sc、Ca修饰的COF-1的储氢性能的研究表明,Ca、Sc在COF-1上的稳定吸附位置也是C六元环的中心,结合能分别为-1.306 e V和-2.708 e V。每个Ca和Sc原子上能吸附4个H₂分子,对H₂分子在Ca、Sc修饰的COF-1上吸附机理研究表明,H₂分子与Ca原子之间为极化作用,而H₂分子与Sc之间除了极化作用外,H₂分子与Sc之间还存在Kubas作用。通过增加金属原子浓度来增加COF-1的储氢量,当Ca、Sc原子覆盖浓度最大时,COF-1上分别能吸附6个Ca、Sc原子,每个Ca、Sc原子同样能吸附4个H₂氢分子,对应的储氢量分别为7.08wt%和6.78 wt%。更多还原

【Abstract】 Hydrogen energy is considered to be an ideal renewable clean energy that can replace traditional fossil fuels in the 21 st century due to its non-pollution,abundant reserves,and high energy storage density characteristics.The storage of hydrogen energy is the key to determine the rapid development of hydrogen energy.In recent years,research on hydrogen storage has mainly focused on hydrogen fuel cell vehicles,but on-board hydrogen storage is still a challenge.COF-1 is a two-dimensional COF structure with the highest adsorption enthalpy in two-dimensional COFs and shows better hydrogen storage performance at low temperature and high pressure.However,the weak van der Waals interaction between the molecule and COF-1 results in poor hydrogen storage performance of COF-1 at room temperature.Metal atoms decoration can significantly improve the interaction between the substrate and hydrogen molecules.Based on the above background,the hydrogen storage properties of metal-decorated COF-1 have been studied by using first principle calculation.By studying the hydrogen storage properties of Li-decorated COF-1,we find the center of the C hexagon ring is the most stable site for Li atom and Li atom can adsorb 3 H2 molecules.At most 6 Li atoms can be adsorbed on COF-1 layer and per Li atom can adsorb 3 H2 molecules stably,namely,18 H2 molecules can be adsorbed on LiCOF-1 with hydrogen capacity of 7.69 wt%.The adsorption of hydrogen molecules on Li-COF-1 is mainly through the electrostatic interaction between the charged Li atoms and the polarized H2 molecules.Ab initio molecular dynamics simulation results show that 6Li-COF-1 can adsorb up to 12 H2 molecules with a hydrogen storage capacity of 5.26 wt%.Studies on the hydrogen storage properties of COF-1 decorated by Sc and Ca atoms show that the stable adsorption sites for Ca and Sc on COF-1 are also the center of the C six hexagon ring,with binding energies of-1.306 e V and-2.708 e V,respectively.Each Ca and Sc atoms can adsorb 4 H2 molecules,and the adsorption mechanism of H2 molecules on Ca and Sc modified COF-1 shows that the interaction between H2 molecules and Ca atoms is polarization interaction.For H2 molecules on Sc-decorated COF-1,in addition to the polarization interactions,there is also a Kubas effect between H2 molecules and Sc.by increasing the concentration of metal atoms to increase the hydrogen storage capacity of COF-1.When Ca and Sc atoms cover the maximum concentration,COF-1 can adsorb 6 Ca and Sc atoms,respectively.Each Ca and Sc atom can also adsorb 4 H2 molecules,the corresponding hydrogen storage capacity of is 7.08 wt% and 6.78 wt%,respectively.更多还原