Record Hydrogen Storage Capacities in Advanced Carbon Storage Materials

Carbons can be engineered to achieve exceptional storage capacities: the ALL-CRAFT (\underline{www.all-craft.missouri.edu}) nanoporous carbon achieves gravimetric excess adsorption of 0.073 kg H$_2$/kg C, gravimetric storage capacity of 0.106 kg H$_2$/kg C, and volumetric storage capacity of 0.040 kg H$_2$/l C (80 K, 100 bar). The nanopores generate high storage capacity by having: high surface area (2,600 m$^2$/g); high H$_2$-wall interaction; and multi-layer H$_2$ adsorption (cryogenic). We we show how the experimental characteristics of the ALL-CRAFT carbon correlate to the observed H$_2$ storage, with help from theoretical considerations and GCMC simulations. The ALL-CRAFT carbon is composed of a large variety of pore sizes which generates substantial heterogeneity. We explain most features observed by considering superpositions of low- and high-binding energy sites (9 kJ and 5 kJ/mol), corresponding to wide and narrow ($<$ 1 nm) pores. We further explain: exceptional low-temperature storage (in excess of the usual Chahine's rule); and absence of an excess adsorption peak (for $0 < P < 100$ bar).