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

Abstract

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 508m2/g and pore volume of 0.68cm3/g wherein micropores account for 80% (407m2/g) of surface area. The carbon aerogel is dominated by micropores of size <15Å with a broad distribution of pores centered at 8 and 12Å. Chemical activation of the carbon aerogel with KOH generates activated carbon aerogels with surface area of 915–1980m2/g and pore volume up to 2.03cm3/g. Activation at 600, 700 or 800°C (and KOH carbon ratio of 2, 4 or 5) yields activated carbon aerogels with micropore size distribution centred at ca. 8 and 13Å (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 <15Å 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 2.7–3.0mmol/g at 25°C and 1bar, and store between 3.5 and 4.3wt% hydrogen at −196°C and 20bar. The hydrogen storage density of the carbons is high (up to 16.2μmol H2m−2) with small micropores favouring high density.