Hydrogen storage in microporous hypercrosslinked organic polymer networks

A series of hypercrosslinked polymer networks has been synthesized by the self-condensation of bischloromethyl monomers such as dichloroxylene (DCX), 4,4′-bis(chloromethyl)-1,1′-biphenyl (BCMBP), and 9,10-bis(chloromethyl)anthracene (BCMA). These materials are predominantly microporous and exhibit Brunauer-Emmett-Teller (BET) surface areas of up to 1904 m²/g as measured by N₂ adsorption at 77.3 K (Langmuir surface area = 2992 m²/g). Networks based on BCMBP exhibit a gravimetric storage capacity of 3.68 wt % at 15 bar and 77.3 K, the highest yet reported for an organic polymer. The micro- and mesostructure of the networks is explained by a combination of solid-state NMR, gas sorption measurements, pycnometry, and molecular simulations. The isosteric heat of sorption for H ₂ on these materials is found to be in the range 6-7.5 kJ/mol. A molecular model is presented for ap-DCX network that simulates well certain key physical properties such as pore volume, pore width, absolute density, and bulk density. This model also predicts the isotherm shape and isosteric heat for H₂ sorption at 77.3 and 87.2 K but overestimates the absolute degree of H2 uptake, most likely because of a degree of occluded, inaccessible porosity in the real physical samples.