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 H2 on these materials is found to be in the range 6−7.5 kJ/mol. A molecular model is presented for a p-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.