Enhanced methane storage of chemically and physically activated carbide-derived carbon

Carbide-derived carbons (CDCs) produced by chlorination of carbides offer great potential for precise pore size control at the atomic level, making them attractive candidates for energy storage media. CDCs activated with CO2 or KOH possess distinct improvements in porosity, displaying specific surface areas above 3000 m2 g−1 and pore volumes above 1.3 cm3 g−1. These correspond to gravimetric methane uptake of 16 wt% at 35 bar and 25 °C, close to the currently best reported material PCN-14, a metal-organic framework (MOF), at 35 bar and 17 °C or KOH activated anthracite at 35 bar and 25 °C. The best excess gravimetric methane uptake is obtained with a TiC-derived CDC activated with CO2 at 975 °C for 2 h, namely a very large surface area of 3360 m2 g−1 resulting in 18.5 wt% at 25 °C and 60 bar. To obtain realistic volumetric methane capacity, the packing density of completely dried CDC was measured, from which we obtain excess capacity of 145 v(STP) v−1 from CDC activated with CO2 at 875 °C for 8 h, 81% of the DOE target (180 v(STP) v−1) at 35 bar and 25 °C. From small-angle X-ray scattering (SAXS) measurements, pore radii of gyration (Rg) between 0.5 nm and 1 nm are determined. Temperature-dependent methane isotherms show that the isosteric heat of adsorption reaches 24 kJ mol−1 at the initial stage of low loading.