Local atomic density of microporous carbons

We investigated the structure of two disordered carbons: activated carbon fibers (ACF) and ultramicroporous carbon (UMC). These carbons have highly porous structure with large surface areas and consequently low macroscopic density that should enhance adsorption of hydrogen. We used the atomic pair distribution function to probe the local atomic arrangements. The results show that the carbons maintain an in-plane local atomic structure similar to regular graphite, but the stacking of graphitic layers is strongly disordered. Although the local atomic density of these carbons is lower than graphite, it is only ∼20% lower and is much higher than the macroscopic density due to the porosity of the structure. For this reason, the density of graphene sheets that have optimum separation for hydrogen adsorption is lower than anticipated.