Topological defects: Origin of nanopores and enhanced adsorption performance in nanoporous carbon

A scanning transmission electron microscopy investigation of two nanoporous carbon materials, wood-based ultramicroporous carbon and poly(furfuryl alcohol)-derived carbon, is reported. Atomic-resolution images demonstrate they comprise isotropic, three-dimensional networks of wrinkled one-atom-thick graphene sheets. In each graphene plane, nonhexagonal defects are frequently observed as connected five- and seven-atom rings. Atomic-level modeling shows that these topological defects induce localized rippling of graphene sheets, which interferes with their graphitic stacking and induces nanopores that lead to enhanced adsorption of H₂ molecules. The poly(furfuryl alcohol)-derived carbon contains larger regions of stacked layers, and shows significantly smaller surface area and pore volume than the ultramicroporous carbon.