Microporous activated carbon aerogels via a simple subcritical drying route for CO2 capture and hydrogen storage

The successful synthesis of carbon aerogels, via a simple subcritical drying route and subsequent activation to high surface area carbons with attractive properties for gas storage is demonstrated. The route generates highly microporous carbon aerogel with a surface area of 508 m(2)/g and pore volume of 0.68 cm(3)/g wherein micropores account for 80% (407 m(2)/g) of surface area. The carbon aerogel is dominated by micropores of size <15 angstrom with a broad distribution of pores centered at 8 and 12 angstrom. Chemical activation of the carbon aerogel with KOH generates activated carbon aerogels with surface area of 915-1980 m(2)/g and pore volume up to 2.03 cm(3)/g. Activation at 600,700 or 800 degrees C (and KOH carbon ratio of 2, 4 or 5) yields activated carbon aerogels with micropore size distribution centred at ca. 8 and 13 angstrom (i.e., similar to that of the starting carbon aerogel) but with a large increase in pore volume arising from the micropores with the effect that pores of size <15 angstrom already present in the starting CA aerogel are retained and enhanced in the activated carbon aerogels; the proportion of microporosity rises from 80% to 87%. The activated carbon aerogels exhibit high CO2 uptake of 2.7-3.0 mmol/g at 25 degrees C and 1 bar, and store between 3.5 and 4.3 wt% hydrogen at -196 degrees C and 20 bar. The hydrogen storage density of the carbons is high (up to 16.2 mu mol H-2 m(-2)) with small micropores favouring high density. (C) 2013 Elsevier Inc. All rights reserved.