Nanospace-engineered carbons for reversible storage of natural gas and hydrogen

Abstract

Early results on optimization of gravim. excess adsorption for undoped carbons, with KOH activation: 1.Excess adsorption and gravimetric storage capacity both increase with increasing KOH:C ratio and activation temperature. Excess adsorption dominated by KOH:C ratio. 2.Volumetric storage capacity decreases with increasing activation temperature. 3. 2.5K activated at 700 oC has record volumetric storage capacity of 132 g CH4/liter carbon at 35 bar and 22 oC (200 V/V, 110% of DOE target of 118 g/liter). Has only micropores (< 2nm). Large surface area and low porosity is key to volumetric storage capacity. 4. 4K activated at 790 oC has record gravimetric storage capacity of 256 g CH4/kg carbon at 35 bar and 22 oC. Presence of mesopores raises gravimetric storage capacity. 5. Langmuir and Ono-Kondo analysis of CH4 excess isotherms at 295 K gives surface area (2400-2700 m2/g, agree with BET area), film thickness (~0.4 nm), saturated film density (320-440 g/cm3), and average binding energy (8-9 kJ/mol). 6.Briquetting can increase volumetric storage capacity by factor of 2 if surface area remains constant.