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

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 m2/g and 1.7 cm3/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 H2 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.