Hypercrosslinked polyanilines with nanoporous structure and high surface area: potential adsorbents for hydrogen storage

A method for the preparation of an entirely new type of nanoporous material, hypercrosslinked polyaniline, with permanent porous structure and specific surface areas exceeding 630 m² g⁻¹ has been developed. The hypercrosslinking reaction was carried out with commercial polyaniline and diiodoalkanes or paraformaldehyde using both conventional and microwave assisted processes. Polyaniline swollen in an organic solvent was hypercrosslinked to form a rigid, mesh-like structure with permanent porosity and a high surface area. The resulting materials were characterized using infrared spectroscopy and elemental analysis. Porous properties were determined by means of scanning electron microscopy as well as nitrogen and hydrogen adsorption. Short crosslinks such as those formed using paraformaldehyde and diiodomethane led to materials with the highest surface areas. Surface area also increased with the concentration of polyaniline in solution used during preparation. The hydrogen storage capacities of these materials were also tested and a capacity of 2.2 wt% at 77 K and 3.0 MPa was found for the best adsorbent. Hypercrosslinked polyanilines exhibit a remarkably high affinity for hydrogen, which results in enthalpies of adsorption as high as 9.3 kJ mol⁻¹ (exothermic), in sharp contrast with hypercrosslinked polystyrenes and metal–organic frameworks for which significantly lower enthalpies of adsorption, typically in the range of 4–7 kJ mol⁻¹, are measured.