Superactivated carbide-derived carbons with high hydrogenstorage capacity

Abstract

Activation of carbide-derived carbon (CDC) with KOH generates superactivated carbons with high surface area (up to 2800 m² g⁻¹). The KOH activation, at a CDC/KOH weight ratio of 1 : 4, was performed at between 600 and 900 °C. Despite a 50% increase in porosity, the activated carbons retain a microporous nature with typically 90% of their surface area and 80% of their pore volume arising from micropores. The small micropores (8–12 Å) of the CDC are retained in the activated carbons, along with the generation of a greater proportion of new 20 Å pores. The size of the larger pores increases slightly at higher activation temperature. The activated carbons exhibit an enhancement of up to 63% in hydrogen uptake from 3.8 wt% for the CDC to 6.2 wt% at −196 °C and 20 bar. At 1 bar the superactivated CDC carbons store 2.7 wt% hydrogen, which is amongst the highest values ever reported for activated carbon. An increase in surface oxygen concentration also contributes to the enhanced hydrogen uptake. For example, activation at 600 °C does not alter the textural properties, but enhances hydrogen uptake by ca. 30% compared to the CDC due to an apparent higher surface oxygen concentration.