Volumetric loading uncovers unexpected patterns in Brunauer-Emmett-Teller area of widely-used carbon materials

This work seeks to clarify the distinction between mass-based and volume-based metrics for adsorption capacity. Since volume plays a critical role in equipment design, minimizing it is essential, meaning that properties expressed per unit volume should be maximized. Nitrogen adsorption (BET area) over carbon materials has been employed to illustrate the concept. Relevant porous carbon materials were evaluated based on their mass and volumetric Brunauer-Emmett-Teller (BET) areas. The volumetric approach provided a very different perspective compared to the mass-based metric. A significant decrease is observed in the 3D-graphene and carbon black, which is due to their low bulk densities. A densely-packed aligned SWCNT yields the top value, which features a very high bulk density and high mass-based BET area. Interestingly, a micro-mesoporous activated carbon (CNR115) exhibits a volumetric BET that closely resemble that of the aligned SWCNT. Though this material has tortuous pores compared to the aligned SWCNT, these contribute to a very high mass-based BET area. Moreover, it possesses a moderately high bulk density. The work proves that the generally-applied mass-based metric may bias and influence the perceived potential of a material, for example as this work shows in terms of adsorption capacity. In other words, comparison on volumetric basis can overturn adsorption capacity rankings. New research avenues have been identified and briefly discussed.