Perpustakaan Digital ITB

Porous carbons represent a typical class of electrode materials forelectric double-layer capacitors. However, less attention has been focused on thestudy of the capacitive mechanism of electrochemically active surface oxygengroups rooted in porous carbons. Herein, the degree and variety of oxygensurface groups of HNO3-modified samples (N-CS) arefinely tailored by a mildhydrothermal oxidation (0.0?3.0 mol L?1), while the micro?meso?macro-porous structures are efficiently preserved from the original sample. Thus, N-CSis a suitable carrier for separately discussing the contribution of oxygen functionalgroups to the electrochemical property. The optimized N-CS shows a highcapacitance of 279.4 F g?1at 1 A g?1, exceeding 52.8% of pristine carbon sphere(CS) (182.8 F g?1at 1 A g?1) in KOH electrolyte. On further deconvoluting theredox peaks of cyclic voltammetry curves, wefind that the pseudocapacitance notonly associates with the surface-controlled faradic reaction at high scan rate butalso dramatically stems from the diffusion-controlled capacitance through potassium and hydroxyl ion insertion/deinsertion intothe underutilized micropores at low scan rate. The assembled supercapacitor based on N-CS presents a stable energy density of5Whkg?1over a wide range of power density of 250?5000 W kg?1, which is higher than 0.0N-CS in KOH electrolyte. InTEABF4electrolyte, the N-CS supercapacitor has an energy density of 26.9 Wh kg?1at the power density of 1350 W kg?1andexhibits excellent cycling stability with a capacitance retention of 93.2% at 2 A g?1after 10 000 cycles. These results demonstratethat surface oxygen groups alter the capacitive mechanism and contribution of porous carbons.