Gram-scale production of vertically aligned holey graphene nanosheet arrays derived from a renewable biomass precursor via a facile hydrothermal/salt-assisted pyrolysis method for aqueous high-performance redox supercapacitors

Abstract

Herein, we developed a facile method for the gram-scale production of high-quality vertically aligned graphene nanosheet arrays (VAGNAs) named as hydrothermal/salt-assisted pyrolysis (HSP) for constructing high-performance redox supercapacitors. VAGNAs were fabricated on a large scale using HSP from low-cost, green and renewable biomass instead of fossil gas precursors; no expensive instrument or extra substrate was required. The key fabrication process parameters were screened and optimized, including the pretreatment method, selected salts and pyrolysis temperature. The as-fabricated VAGNAs exhibit outstanding properties, including high graphitization degree, thin nanosheets, good hydrophilicity and a hierarchically porous structure. The as-fabricated VAGNAs were employed as electrodes to construct redox supercapacitors. The VAGNA electrodes possess an ultrahigh specific capacitance of 3148 F g⁻¹ in 1.0 M KOH electrolyte with the addition of 0.10 M K₃Fe(CN)₆. The assembled symmetrical redox supercapacitor based on VAGNA-L-1000 delivers a high specific capacitance of 92.8 F g⁻¹ at 1 A g⁻¹ under a wide operation potential window of 2.0 V and high energy density of 36.7 W h kg⁻¹ at a power density of 712 W kg⁻¹. The present study highlights the large-scale synthesis of high-value added nanocarbons derived from renewable biomass for developing high-performance supercapacitors with high energy density in an economical way.