Hierarchically porous nitrogen-doped carbon (HPNC) with a helically arranged rodlike structure has been synthesized by in situ growth of ZIF-8 (zeolitic imidazolate frameworks) nanoparticles on cellulose nanocrystals (CNC), which simultaneously acts as both a self-template and a carbon source, and controls the growth of ZIF-8 coated CNC, and a subsequent carbonization. Because of the novel structural characteristic and satisfying chemical composition of the HPNC, it exhibits an improved capacitance of 172 F/g at 100 mA/g, superior energy density of 23.75 Wh/kg at a power density of 50 W/kg and 14.58 Wh/kg at 5000 W/kg, respectively, and long cycling stability (retention 94.5% after 5000 cycles) in aqueous KOH solution. Further, a symmetric supercapacitor is constructed and displays significantly increased electrochemical performance, demonstrating high specific capacity (∼100 F/g at 0.2 A/g and ∼74 F/g at 5.0 A/g, respectively), impressive rate performance (∼70 F/g at 10 A/g), and excellent stability with a capacitance retention of ∼81% over 5000 cycles. Moreover, this facile, yet effective, low cost, eco-friendly, and sustainable preparation approach for construction of metal-free porous electrodes from abundant biomass carbon can be applicable to other electrode materials for a wide range of applications.
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Wang et al. (2018) studied this question.