This paper demonstrates that nanospace engineering of KOH activated carbon is possible by controlling the degree of carbon consumption and metallic potassium intercalation into the carbon lattice during the activation process. High specific surface areas, porosities, sub-nanometer (<1 nm) and supra-nanometer (1-5 nm) pore volumes are quantitatively controlled by a combination of KOH concentration and activation temperature. The process typically leads to a bimodal pore size distribution, with a large, approximately constant number of sub-nanometer pores and a variable number of supra-nanometer pores. We show how to control the number of supra-nanometer pores in a manner not achieved previously by chemical activation. The chemical mechanism underlying this control is studied by following the evolution of elemental composition, specific surface area, porosity, and pore size distribution during KOH activation and preceding H(3)PO(4) activation. The oxygen, nitrogen, and hydrogen contents decrease during successive activation steps, creating a nanoporous carbon network with a porosity and surface area controllable for various applications, including gas storage. The formation of tunable sub-nanometer and supra-nanometer pores is validated by sub-critical nitrogen adsorption. Surface functional groups of KOH activated carbon are studied by microscopic infrared spectroscopy.

This paper covers the optimization of methane volumetric storage capacity by controlling the sub-nanometre (<1 nm) and supra-nanometre (1-5 nm) pore volumes. Nanospace engineering of KOH activated carbon generates an ideal structure for methane storage in which gas molecules are adsorbed as a high-density fluid by strong van der Waals forces into pores that are a few molecules in diameter. High specific surface areas, porosities, subnanometre (<1 nm) and supra-nanometre (1-5 nm) pore volumes are quantitatively selected by controlling the degree of carbon consumption and metallic potassium intercalation into the carbon lattice during the activation process. The formation of tuneable sub-nanometre and supra-nanometre pores is validated by sub-critical nitrogen adsorption. Aberration-corrected scanning transmission electron microscopy data show the atomic structure of highsurface-area activated carbon (2600 m 2 /g). While high surface area and high porosity are optimal for gravimetric methane storage, the results indicate that an exclusive sub-nanometre region, a low porosity and an acceptable surface area (approximately 2000 m 2 /g) are ideal for methane volumetric storage, storing 120 g CH 4 /l (184 vol/vol) at 35 bar and room temperature (22 ˚C). High-pressure methane isotherms up to 150 bar at 30, -25 and -50 °C on optimal activated carbons are presented. Methane volumetric storage capacity at 35 bar reaches 176 g/l (269 vol/vol) and 202 g/l (309 vol/vol) at -25 and -50 °C, respectively.

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

This work investigates the effects of neutron irradiation on nitrogen and hydrogen adsorption in boron-doped activated carbon. Boron-neutron capture generates an energetic lithium nucleus, helium nucleus, and gamma photons, which can alter the surface and structure of pores in activated carbon. The defects introduced by fission tracks are modeled assuming the slit-shaped pores geometry. Sub-critical nitrogen adsorption shows that nitrogen molecules cannot probe the defects created by fission tracks. Hydrogen adsorption isotherms of irradiated samples indicate higher binding energies compared to their non-irradiated parent samples.

Adsorbed natural gas (ANG) technology is an energy-efficient method for storing natural gas at room temperature and low pressure. The search for high-storage-performance natural gas sorbents for gaseous fuels is currently pursued by numerous research groups worldwide. While research in this field is mainly devoted to optimizing the gravimetric and volumetric storage capacity of methane, this work investigates the long-term effect of large alkanes on natural gas storage. This article investigates the evolution of storage capacity and gas composition during adsorption/desorption cycles at room temperature (charge/discharge of an ANG tank) and at various elevated temperatures (regeneration of tank) on a commercial, high-surface-area activated carbon (Maxsorb MSC-30, Kansai Coke and Chemical Co. Ltd.). Cycling and regeneration study of sorbent for hundreds of cycles has been investigated. The evolution of storage capacity is measured after successive cycling using a custom-built Sievert apparatus. For natural gas, gravimetric excess adsorption drops to 33% in the first 100 cycles and continues to decrease slowly until it reaches 25% by the 1000th cycle. Volumetric storage capacity shows a deterioration of 50% after 100 cycles and remains approximately constant after that. The contaminant gas composition is measured as a function of successive cycling using gas chromatography. Finally, efficient regeneration techniques have been tested to allow a continuous operation for thousands of cycles.