A First-principles Study On The Hydrogen Storage Performance Of Metal-modified Covalent Organic Framework COF-1

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.