Open carbon frameworks - a search for optimal geometry for hydrogen storage

Abstract

Properties of a new class of hypothetical high-surface-area porous carbons (open carbon frameworks) have been discussed. The limits of hydrogen adsorption in these carbon porous structures have been analyzed in terms of competition between increasing surface accessible for adsorption and the lowering energy of adsorption. From an analysis of an analytical model and simulations of adsorption the physical limits of hydrogen adsorption have been defined: (i) higher storage capacities in slit-shaped pores can be obtained by fragmentation/truncation of graphene sheets into nano-metric elements which creates surface areas in excess of 2600 m2/g, the surface area for infinite graphene sheets; (ii) the positive influence of increasing surface area is compensated by the decreasing energy of adsorption in the carbon scaffolds of nano-metric sizes; (iii) for open carbon frameworks (OCF) built from coronene and benzene molecules with surface areas 6500 m2 g-1, we find an impressive excess adsorption of 75–110 g H2/kg C at 77 K, and high storage capacity of 110–150 g H2/kg C at 77 K and 100 bar; (iv) the new OCF, if synthesized and optimized, could lead to required hydrogen storage capacity for mobile applications.