Open Carbon Frameworks (OCF): new hypothetical ordered carbons for hydrogen storag
Résumé
One of potential perspectives for clean fueling of cars is the use of hydrogen-powered fuel cells. A major challenge in the massif implementation of hydro-gen-fuelled vehicles still consist in designing hydrogen storage systems that are reversible, light, cheap and able of delivering a driving range of few hundreds of kilometers.
Between the possible hydrogen adsorbents carbon porous structures with locally slit-shaped pore geometry remain the most promising ones.
It has been shown in the past that it is not possible to increase hydrogen storage capacity by modification of slit width only, without simultaneous in-crease of the specific surface. Here, we propose new models of hypothetical all-carbon with specific surfaces higher than that of graphene. We call them Open Carbon Frameworks, OCF (Fig.1). The structures are ordered, and have low density architecture required for effective applications for mobile storage. Theoretically they may have the specific surfaces exceeding 6000 m2/g.
From the analysis of the computer simulations of adsorption properties of the new structures, a rich spectrum of relations between structural characteristics of OCFs and ensuing hydrogen adsorption (structure-function relations) emerg-es: (i) storage capacities higher than in slit-shaped pores can be obtained by fragmentation/truncation of graphene sheets, which creates additional surface areas (with respect to infinite graphene sheets), carried mainly by edge sites; ii) for OCFs with a ratio of in-plane to edge sites approximately equal 1 and sur-face areas of 3800-6500 m2/g, we found at 77 K record maximum excess ad-sorption of 75-85 g H2/kg C, and record storage capacity of 100-260 g H2/kg C (at 100 bar); (iii) additional increase of hydrogen uptake could potentially be achieved by chemical substitution and/or intercalation of OCF structures, in or-der to increase the energy of adsorption. In consequence we conclude that OCF structures, if synthesized, will allow the hydrogen uptake at the level re-quired for vehicular applications.