Modification of COF-108 via impregnation/functionalization and Li-doping for hydrogen storage at ambient temperature

Abstract

Post-modification approaches such as Li-doping, impregnation, and functionalization are promising methods to enhance H2 adsorption in metal–organic frameworks (MOFs) and covalent-organic frameworks (COFs). In this work, we propose a two-step method to modify COF-108 with the aim to enhance its hydrogen storage capacity at ambient temperature. First, we geometrically modified COF-108 through C60 impregnation or aromatic ring grafting. Subsequently, we surface doped the modified COF-108 with Li atoms. COF-108 is the lightest 3D crystalline material ever reported and it is a promising H2 storage material. Our grand canonical Monte Carlo (GCMC) simulations demonstrated that the combination of Li-doping with C60 impregnation or aromatic ring grafting can potentially increase the volumetric H2 adsorption capacity of COF-108 to reach a total H2 adsorption capacity close to the U.S. DOE target. One of the Li-doped C60-impregnated (Li6C60) COF-108 (with 8 Li6C60 moieties impregnated) showed an absolute H2 uptake beyond the 2010 DOE target (45.6 mg/g and 28.6 g/cm3) at 233 K and 100 bar. Impregnation of C60 and/or grafting of aromatic rings not only increased the density of doped Li in the modified COF-108 but also created more overlapped potential interaction with H2, which resulted in higher number of H2 adsorption sites per unit volume as compared to the unmodified material.