Covalent organic frameworks (COFs) are considered as a new type of adsorbing material for hydrogen. In this work

density functional theory (DFT) has been applied to investigate the adsorption mechanism of H2 on seven main clusters of COFs

and GGA/PBE is used in the calculation. The results indicate that the center of benzene ring is the most favorable site when H2 molecular attacks vertically

in addition the center and oxygen atom of B3O3 ring are more favorable when H2 molecular attacks parallelly. The increase of carbon atom number on organic cluters would be beneficial for adsorption of H2. By calculation of different adsorption configurations for two H2 molecules on COF-10 and COF-105

it is found that a cooperative effect between H2 adsorption on these two COFs could be exist. Doping of alkali metals (Li

Na

K) and substitution of organic functional groups (methyl

sulfhydryl

amino) on COFs can significantly enhance the adsoroption energy

indicating that these chemical modifications are an effective way for enhancement of hydrogen adsorption capacity of COFs.