Preparation of activated carbons from corncob with large specific surface area by a variety of chemical activators and their application in gas storage

Abstract

Activated carbons were produced from agricultural waste corncob using a variety of different activation strategies and activators. The BET specific surface area and pore volume of the carbons produced by a two-step KOH activation process were 3012 m 2/g and 1.7 cm 3/g, respectively. All carbons prepared showed a microporous character, except for that prepared by a one-step phosphorous acid activation which exhibited hysteresis of a mesoporous carbon. The hydrogen adsorption performance of the different carbons was closely investigated. The microporous carbon with the largest BET specific surface area showed H 2 adsorption capacities up to 2.0 wt% at 77 K under 1 atm pressure and 0.44 wt% at 298 K at 5 MPa. The adsorption isotherm model based on the Langmuir–Freundlich equation together with Soave–Redlich–Kwong equation of state for determination of the gas phase fugacity provided a satisfactory representation of the high pressure hydrogen data. The parameter representing full coverage of the solid surface from the Langmuir–Freundlich equation is 9.73 mmol/g or 2 wt% at 298 K. The carbon with the largest hydrogen uptake capacity still cannot meet the US DOE target for hydrogen storage of 6 wt%. The isosteric heat of adsorption of carbon was 7 kJ/mol, typical of a physisorption character and in agreement with literature for the hydrogen–carbon interaction.