Low-dosage KOH assisted activation for preparation of sodium humate-based porous carbon electrodes for supercapacitors

Abstract

With the miniaturization of electronic devices and the increase of their high-capacity requirements, higher demands are put forward for energy storage devices, and for supercapacitors, the selection of suitable carbon materials is extremely critical. The oxygen-doped hierarchical porous carbon has better surface wettability, which can reduce the transport resistance of ions between the electrolyte and the surface of the electrode materials and provide active sites to improve the specific capacitance. In this paper, the oxygen-rich hierarchical porous carbon was prepared by using sodium humate with rich oxygen functional groups as the precursor and using a low-dosage of KOH to assist the activation of the carbon skeleton to regulate the pore structure and oxygen content of porous carbon materials. The results showed that the obtained carbon material of HPC-2 had high oxygen content (19.93 atom%) and high specific surface area (1020.34 m² g⁻¹) with a sample/KOH mass ratio of 1 : 0.5. In the three-electrode system, the specific capacitance of the HPC-2 carbon electrode material was 253.3 F g⁻¹ at a current density of 0.5 A g⁻¹. The assembled symmetric supercapacitor possesses an energy density of 11.2 W h kg⁻¹ at a power density of 74.3 W kg⁻¹ and exhibits excellent cycle stability with a retention rate of 93.6% and a coulombic efficiency of 97.8% after 10 000 cycles at 5 A g⁻¹. The preparation of hierarchical porous carbon electrode materials for high-performance supercapacitors with low-dosage KOH assisted activation of sodium humate is environmentally friendly.