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

• Highly microporous carbon aerogels are prepared via simple subcritical drying.
• Surface area of activated carbon aerogels up to 1980 m2/g with 87% from micropores.
• Activated carbon aerogels exhibit high CO2 uptake of 3.0 mmol/g at 25 oC and 1 bar.
• Activated carbon aerogels store between 3.5 and 4.3 wt% H2at –196 oC and 20 bar.  
• High CO2 and H2 uptake density up to 2.95 mmol/m2 and 16.2 μmol/m2, respectively.

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 m2/g and pore volume of 0.68 cm3/g wherein micropores account for 80% (407 m2/g) of surface area. The carbon aerogel is dominated by micropores of size <15 Å with a broad distribution of pores centered at 8 and 12 Å. Chemical activation of the carbon aerogel with KOH generates activated carbon aerogels with surface area of 915–1980 m2/g and pore volume up to 2.03 cm3/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 13 Å (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 Å 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 °C and 1 bar, and store between 3.5 and 4.3 wt% hydrogen at −196 °C and 20 bar. The hydrogen storage density of the carbons is high (up to 16.2 μmol H2 m−2) with small micropores favouring high density.

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