A multiscale theoretical method, which combines the first-principles calculation and grand canonical Monte Carlo (GCMC) simulation, is used to investigate the adsorption capacities of hydrogen in nondoped and Li-doped covalent organic borosilicate frameworks (COF-202). Our simulations indicate that the total gravimetric and volumetric hydrogen uptakes of COF-202 reach 7.83 wt % and 44.37 g/L at T = 77 K and p = 100 bar, respectively. To enhance the hydrogen storage capacity of COF-202, the doping of Li atoms in COF-202 is studied systematically. First, the first-principles calculations are performed to investigate the possible adsorption sites and the quantity of Li atoms doped in COF-202. Our results prove that, for a single Li atom, the top of the phenyl groups in COF-202 is the most favorable adsorption site; for coadsorption of two Li atoms, with one adsorbed at the top site of a phenyl group and the other at its neighboring interstitial site between the phenyl group and the B-O-Si linkage is the most favorable adsorption mode. Our GCMC simulations predict that the total gravimetric and volumetric uptakes of hydrogen in the Li-doped COF-202 reach 4.39 wt % and 25.86 g/L at T = 298 K and p = 100 bar, respectively, where the weight percent of Li equals to 7.90 wt %. This suggests that the Li-doped COF-202 is one of the most promising candidates for hydrogen storage at room temperature.
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