Synthesis of microporous boron-substituted carbon (BCx) materials for hydrogen physisorption

This paper discusses a new synthesis route to prepare boron substituted carbon (BCx) materials containing 3-15% B content and microporous microstructure. The BCx materials show a significantly higher hydrogen binding energy (10-20 kJ/mol)and physisorption capacity (2-3 times increase), compared with the corresponding carbonaceous (C) materials. Both enhancements are directly associated with B content and the acidity of B moiety. The chemistry involves a pyrolysis of the designed boron-containing polymeric precursors with the specific B contents. During pyrolysis, most of the boron moieties in the precursor were transformed into BCx material with the structure changing from puckered to graphitic controlled by pyrolysis temperature. On the other hand, the in situ formed by-products created a micro-porous structure. The micro-porous BCx material with B content >7% and surface area >700 m2/g 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 high binding energy of hydrogen molecules.