The synthesis, characterization, and performance of a new low pressure, monolithic, activated carbon adsorbent developed for methane storage is discussed and compared to other adsorbents. The effect of particle packing density on the storage capacity of tanks filled with commercially available and developmental adsorbents is quantified. 20 kg of the developed monolithic material is tested using a custom built, 40 L, space conformable tank test assembly. The performance is found to be superior to metal organic frameworks and other activated carbons reported in literature based on high tank volumetric and gravimetric storage capacities. The developed material has a pore structure and external dimensions that allow for rapid adsorption/desorption with gas being able to reach the center of the 40 L tank within ~3 s. The developed material delivers 151 V/V of methane between 35 bar and 1 bar in the 40 L tank. A continuous discharge flow rate of 2 g/s at 5 bar for a 10 gge system was demonstrated. 42benefits outweigh its costs. 43The performance of an adsorbent is often 44 measured by collecting an excess adsorption 45 STP/cm 3 at 35 bar by Mason et al[8]) but this 106 material has a fragile pore structure making it 107 difficult to pack efficiently. In Mason's 108 work[8], STP is defined by 0 °C and 1 atm 109 giving a molar density of 0.0446 mol/L. 110 HKUST-1 tablets have a storage capacity of 111 67 g/L[8] which translates to an effective 112 packing fraction (i.e. calculated by using 113 equation 3 and assuming the pore structure is 114unchanged) of 0.31. Tap density 115 measurements (measured according to[22]) on 116 commercially available HKUST-1 produce a 117 packing fraction of 0.51. MIL-53 ( 118 , [8,23]) has a 119 bulk density of 0.4 g/cm 3 (when sold as 120 Basolite ® A100). This equates to a packing 121 fraction of 0.41 and a tank storage capacity of 122 55 g/L. It can be deduced that Tagliabue et 123 al[24] experienced similar packing results 124 (effective packing of 0.34) when trying to 125 densify Ni-MOF-74. Collectively, these 126 results suggest that many MOFs have large 127 crystalline storage capacities (e.g. 161 g/L) 128 but improved material packing methods are 129 required to improve the useable storage 130 capacity of these materials. 131 Experiments on PACs suggest that they can 132 be efficiently packed. Corn cob based KOH 133 PACs produced at the University of Missouri 134 (MU)[12,25,26] demonstrate tank volumetric 135 FIGURE. 14. Volumetric and gravimetric 595 storage and delivery comparisons between the 596 monoliths created here (Monolith-0311) and a 597

Here we report a phase transition in H adsorbed in a locally graphitic Saran carbon with subnanometer pores 0.5-0.65 nm in width, in which two layers of hydrogen can just barely squeeze, provided they pack tightly. The phase transition is observed at 75 K, temperatures far higher than other systems in which an adsorbent is known to increase phase transition temperatures: for instance, H melts at 14 K in the bulk, but at 20 K on graphite because the solid H is stabilized by the surface structure. Here we observe a transition at 75 K and 77-200 bar: from a low-temperature, low-density phase to a high-temperature, higher density phase. We model the low-density phase as a monolayer commensurate solid composed mostly of para-H (the ground nuclear spin state, S = 0) and the high-density phase as an orientationally ordered bilayer commensurate solid composed mostly of ortho-H (S = 1). We attribute the increase in density with temperature to the fact that the oblong ortho-H can pack more densely. The transition is observed using two experiments. The high-density phase is associated with an increase in neutron backscatter by a factor of 7.0 ± 0.1. Normally, hydrogen produces no backscatter (scattering angle >90°). This backscatter appears along with a discontinuous increase in the excitation mass from 1.2 amu to 21.0 ± 2.3 amu, which we associate with collective nuclear spin excitations in the orientationally ordered phase. Film densities were measured using hydrogen adsorption. No phase transition was observed in H adsorbed in control activated carbon materials.

Fabricate high-surface-area, multiply surface-• functionalized carbon ("substituted materials") for reversible hydrogen storage with superior storage capacity (strong physisorption). Characterize materials and storage performance. • Evaluate efficacy of surface functionalization, experimentally and computationally, for fabrication of materials with deep potential wells for hydrogen sorption (high binding energies). Optimize gravimetric and volumetric storage • capacity by optimizing pore architecture and surface composition ("engineered nanospaces").

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