In a recent study, published in the journal Nanotechnology, scientists at the University of Missouri, US, have demonstrated that such control is possible. Carbons chemically activated with potassium hydroxide (carbon oxidation; intercalation of metallic potassium into carbon lattice) gave bimodal pore-size distributions with a large, approximately constant number of sub-nm pores and variable number of supra-nm pores (1–5 nm, peaked around 1.5 nm). The control variables were the KOH:C mass ratio and activation temperature.

Tunable pore space

The team showed that supra-nm pores are absent when the KOH:C ratio and activation temperature are low, and increase rapidly in number with increasing KOH:C ratio and activation temperature. By appropriate choice of the variables, the volume in supra-nm pores can be varied anywhere from 0 to 1.0 cm3/g, while the volume in sub-nm remains approximately 0.6 cm3/g.

This tunable pore space will allow researchers to selectively optimize carbons for high volumetric or high gravimetric storage capacity, depending on the requirements in different vehicles for on-board storage of hydrogen and natural gas.

High volumetric capacity is important for designs where space is limited (passenger vehicles - light duty vehicles) and a high gravimetric capacity is key when vehicle weight must be kept to a minimum.

Further details can be found in the journal Nanotechnology.