High Yield and Packing Density Activated Carbon by One-Step Molecular Level Activation of Hydrophilic Pomelo Peel for Supercapacitors

Abstract

Highly hydrophilic pomelo peel is used as an activated carbon (AC) precursor so that KOH can be homogeneously absorbed within it. Subsequent cryodesiccation retains the original morphology of the pomelo peel and distribution of KOH, which provides the precondition of the one-step molecular level activation. The resulting AC has a high yield of 16.7% of the pomelo peel. The specific surface area of the AC prepared by the one-step molecular activation of cryodesiccated mixture of pomelo peel and KOH (CAC-1) is 1870 m 2 g −1 , which is higher than that of the AC by the one-step activation of oven-dried mixture (AC-1) and AC by the two-step calcination (AC-2). CAC-1 has the highest specific capacitance of 219 F g −1 at 1 A g − 1 among all the three samples. Importantly, the CAC-1 electrode has a high packing density of 0.63 g cm −3 . The aqueous supercapacitor based on CAC-1 has a volumetric cell capacitance of 30.7 F cm −3 , which corresponds to 123 F cm −3 for a single electrode. When the ionic liquid of 1-ethyl-3-methyl-imidazolium tetrafluoroborate is used as electrolyte, CAC-1 shows maximum specific energy of 40.5 Wh kg −1 and energy density of 25.5 Wh l −1 .