Lithium‐Doped 3D Covalent Organic Frameworks: High‐Capacity Hydrogen Storage Materials

Abstract

Quick on the uptake: A multiscale theoretical method predicts that the gravimetric adsorption capacities of H2 in Li‐doped covalent organic frameworks based on the building blocks shown (Li violet, H white, B pink, C green, O red, Si yellow) can reach nearly 7 % at T=298 K and p=100 bar, suggesting that these Li‐doped materials are promising adsorbents for hydrogen storage.magnified image

Doping of Alkali, Alkaline-Earth, and Transition Metals in Covalent-Organic Frameworks for Enhancing CO2 Capture by First-Principles Calculations and Molecular Simulations

“…As mentioned above, there are a series of possible adsorption sites in COFs for metal atoms. Because the configuration of Li adsorption in COFs has been studied extensively, 29 we just discuss the possible adsorption sites and the corresponding binding energies of the other two alkali metals, Na and K, in this section. Figure 4 gives all the optimized adsorption geometries of Na in COFs derived from our first principles calculations.…”

“…If a Li atom is loaded at site ␥ on the HHTP building block, it will also be positively charged as is proved in our previous work due to the charge transfer to the surface. 29 Figure 11b displays the optimized structure, from which it is found that the adsorbed three CO 2 molecules lie simultaneously on the surface with one end toward the Li cation. The distances of the Li cation to the nearest O in CO 2 are 2.118, 2.114, and 2.130 Å, respectively.…”

“…Adsorption of CO 2 in Li-Doped COFs at T ‫؍‬ 298 K. On the basis of the above work, we further predicted adsorption of CO 2 in the Li-doped COFs at room temperature. The doping scheme of Li in COFs can be referred to our previous work, 29 in which all the Li atoms are positively charged. In our distribution scheme, eight Li atoms are placed at site ␣ and ␦ on the TBPM or TBPS building block, respectively, as is shown in Figure 14, while just one Li atom is placed at site ␥ on the HHTP building block.…”

“…As the pressure increases to 5 bar, the gravimetric CO 2 uptakes of the Li-doped COF-102 and COF-105 are 841 and 703 mg/g, respectively, still significantly higher than the nondoped materials. Note that the gravimetric CO 2 uptakes of the Li-doped COF-105 is far from saturation at low and moderate pressures due to its exceptional large free volume (88.42%) 29 and low density (0.18 g/cm 3 ). In particular, at p ϭ 40 bar, the excess gravimetric uptake of CO 2 in Li-doped COF-105 reaches 2266 mg/g, while it is 1773 mg/g for the nondoped COF-105.…”

“…Here, V free was calculated as the volume within one unit cell, where the potential energy of interaction of a hydrogen molecule with the solid framework is less than 10 4 K. The calculated free volumes for the adsorbents studied here were reported in our previous works. 29 …”