Synthesis of micro-porous boron-substituted carbon (B/C) materials using polymeric precursors for hydrogen physisorption

This paper discusses a novel route to prepare porous boron substituted carbon (B/C) materials that show a significantly higher hydrogen binding energy and physisorption capacity, compared with the corresponding carbonaceous (C) materials. The chemistry involves a designed boron-containing polymeric precursor, which is the polycondensation adducts between BCl₃ and lithiated phenylene diacetylene. During pyrolysis, most of the boron moieties in the precursor were transformed into a B-substituted C fused ring structure, and the in situ formed LiCl by-products created a porous morphology. The resulting porous B/C material with 7% B content and 700 m²/g surface area has been prepared, which shows a reversible hydrogen physisorption capacity of 0.6 and 3.2 wt% at 293 and 77 K, respectively, under 40 bars hydrogen pressure. The physisorption results were further warranted by absorption isotherms and in situ ¹H NMR studies, indicating a binding energy of hydrogen molecules of about 11 kJ/mole, significantly higher than the 4 kJ/mole reported on most C surfaces.