The synthesis and characterization of a super-activated carbon containing substitutional boron (BCx) and its applications in hydrogen storage

Abstract

A new family of porous boron-substituted carbon (BCx) materials with controlled structure is investigated. The chemistry involves a B-precursor polymer, i.e., poly(borachlorophenyldiacetylene), containing inorganic additives (templates). At pyrolysis <400°C, the B-precursor engages in easy inter-chain reactions to form dark solid with high yield (>85%). Above 600°C, the amorphous carbon-like BCx materials containing up to 12% B have been prepared, which show an extended fused hexagonal ring structure with B-puckered curvature. This out of planar B moiety maintains its electron deficiency, due to limited π-electron delocalization, and exhibits super-activated properties to enhance H2 binding energy (20–10kJ/mol) and adsorption capacity. After removing the inorganic additives by water-washing, the resulting porous BCx shows a surface area 500–800m2/g. Evidently, the pore size distribution is directly related to melting temperature and distribution of the inorganic salts. As the temperature increases to >1400°C, the distorted ring structure gradually flatten out to form a multi-layer (crystalline) BCx structure. The resulting planar graphitic layer only can accommodate a reduced B content (<3% at 1800°C) and low surface area. The B moieties also lose their acidity due to the extensive π-electron delocalization.