Preparation of Oxygen-enriched Activated Carbons from Coal-based Humic Acids by Zinc Chloride Activation
Oxygen-enriched activated carbons (ACs) for electrochemical capacitors
(ECs) were prepared from coal-based humic acids (HAs) by zinc chloride (ZnCl2)
activation. The effects of ZnCl2/HAs ratio and activation temperature on the characteristics
of ACs were investigated by nitrogen adsorption at 77K, scanning electron microscope, transmission electron microscope
and X-ray photoelectron spectroscopy. The electrochemical performances of ECs with ACs as electrode in a 3M
KOH aqueous solution were evaluated by galvanostatic charge-discharge, cyclic voltammetry and Nyquist impedance
spectroscopy. The results indicate that the optimum conditions for preparing ACs from coal-based HAs are ZnCl2/HAs ratio
of 2.0 and activation temperature of 500 °C. The AC as electrode for ECs prepared under these conditions presents a
high specific capacitance of 226 F/g at a high current density of 5 A/g, and exhibits good cycling stability and minimal resistance.
The excellent electrochemical performances of ACs are attributed to three aspects: the well-developed porosity
with moderate specific surface area, three-dimensional interconnected pore structure and the oxygen-enriched functional
groups in carbon network.
Keywords: Activated carbons, electrochemical capacitors, electrochemical performance, humic acids.
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