Characterization of Activated Carbons Prepared from Almond Shells and Their Hydrogen Storage Properties

In this study, activated carbons with a well-developed porous structure and high surface area were prepared from almond shells by chemical activation using zinc chloride and microwave irradiation methods under a nitrogen atmosphere. The effects of microwave irradiation times, powers, agent ratios on pore volumes, and BET surface areas of the activated carbons were investigated. Pore volumes and BET surface areas of the activated carbons were determined using a BET surface area device; surface functional groups using an FTIR-ATR spectroscope; surface morphology using an SEM/EDX device; and hydrogen storage capacities using an IMI PSI gas storage device. Both the BET surface areas and total pore volumes of activated carbons with increasing microwave irradiation time, power, and agent ratio increased. Experimental studies showed that AC600 with the highest BET surface area (1307 m2/g) and total pore volume (1.66 cc/g) had the highest hydrogen storage capacity (2.53 wt %) at 77 K. FTIR-ATR and SEM analyses indicated that the morphology of the almond shell changed with ZnCl2 activation and the microwave process and it transformed into a carbon-like structure. The hydrogen storage capacity of activated carbons at cryogenic temperature was higher than that at room temperature. The adsorption data were correlated reasonably well by Freundlich adsorption isotherms.