The effects of surface modification on the supercapacitive behaviors of carbon derived from calcium carbide

The capacitive behaviors of calcium-carbide-derived carbon (CCDC) before and after nitric acid (HNO₃) modification are investigated. The structure and morphology of the HNO₃-modified CCDC (M-CCDC) are examined by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The performances of the supercapacitor using M-CCDC as electrode active material are studied by cyclic voltammetry, galvanostatic charge/discharge, electrochemical impedance spectroscopy, and cycle life measurements. The results show that the capacitance of the supercapacitor increases from 154.7 to 196.5 F g⁻¹ and the capacitance decay is only 1.3% over 10,000 cycles for the M-CCDC, which exhibits higher capacitive performance than the pristine CCDC electrode in the aqueous electrolyte solution. The superiority of the M-CCDC in capacitance properties is caused by the variations of surface wettability and the interstitial pore structure of CCDC, which results from the introduction of polar oxygen functional groups onto the CCDC surface by HNO₃ modification.