Preparation and Electrocapacitive Properties of Hierarchical Porous Carbons Based on Loofah Sponge

Four porous carbon samples denoted as LSC-1, LSC-2, LCS-3, and LSC-4 were prepared by carbonization of loofah sponge pretreated by ZnCl₂ activation, immersion in N,N-dimethylformamide (DMF), DMF-assisted solvothermal and melamine-assisted hydrothermal processes, and the specific surface areas were 1007, 799, 773, and 538 m²·g^-1 with mainly micropores, respectively. Electrocapacitive properties of four porous carbon-based electrodes were investigated with cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy in symmetric supercapacitors. All the cyclic voltammetries of four types of supercapacitors showed a rectangular shape, even under a high scan rate of 500 mV·s^-1. The capacitances of LSC-1, LSC-2, LSC-3, and LSC-4 were 107.4, 92.5, 60.3, and 82.3 F·g^-1 at the current density of 0.1 A·g^-1, respectively, and LSC-1 displayed the excellent capacitance retention of about 81.3% with a current density up to 5 A·g^-1. All supercapacitors showed excellent electrochemical stability, and the LSC-1-based supercapacitor showed a cycle stability with 92.6% capacitance retention after 5000 cycles at 1 A·g^-1. The structure-property relationship of LSC samples is discussed and analyzed on the basis of the experimental data.