Studies On Biomass-based Hierarchically Porous Carbon Electrodes And Electrochemical Performances Of Their Supercapacitors

Supercapacitors play an important role in the efficient development of clean and renewable energy.In recent years,biomass-based porous carbon materials were widely used to fabricate high-performance supercapacitors because of their abundant resource and environmental friendliness.Among various biomass materials,wood-derived materials have become ideal precursors for the preparation of hierarchically porous carbon electrodes because of their hierarchically porous structures,low tortuosity,abundant resources and renewability.To improve the electrochemical performances,herein,fir wood carbon materials with regular pore structure were chemically activated and coated with active materials to generate hierarchically porous wood-derived carbon electrodes with high areal capacitances,superior rate performance and outstanding cyclic stability for high-performance supercapacitors.The concrete contents are as below:1.Graphene/carbonized woods activated with ZnCl₂and decorated with NiCo₂O₄for asymmetric supercapacitors:To overcome the disadvantages of inferior areal capacitance and poor hydrophilicity of pure wood carbon electrode,high-performance asymmetric supercapacitors are assembled on the basis of graphene/wood-derived carbon.Herein,hierarchically porous graphene/wood-derived carbon（GWC）aerogels are fabricated by chemical reduction of graphene oxide/wood hydrogels followed by directional-freezing,freeze-drying,and carbonization.An activated GWC（AGWC）anode is prepared by activating the GWC with ZnCl₂to create more mass transport paths and increase wettability,and exhibits a superior areal capacitance of 10965 m F cm^-2(183 F g^-1).An NCO@GWC cathode is synthesized by in situ growth of NiCo₂O₄in the channels of the GWC to produce high pseudocapacitance and improve cycle performance,and exhibits a superior capacitance of 8540 m F cm^-2(854 F g^-1).RGO aerogels are introduced to improve the loading and structural stability of the NiCo₂O₄nanosheets.The assembled NCO@GWC//AGWC asymmetric supercapacitor exhibits a superior areal capacitance of 7116 m F cm^-2,a high volumetric power density of11.8 m W cm^-3,a high volumetric energy density of 4.9 m Wh cm^-3and an excellent cyclic stability of 100%capacitance retention over 1000 cycles at 10 m A cm^-2.2.Self-supported and hierarchically porous activated carbon nanotube/carbonized wood electrodes for high-performance solid-state supercapacitors:To explore the effects of activator on the hierarchically porous architecture of wood carbon and further enhance the electrochemical performances,high-performance supercapacitors are assembled on the basis of carbon nanotube/wood-derived carbon.Carbon nanotubes are introduced to provide large specific surface area,continues electron transport and excellent chemical stability.The hierarchically porous channels with low tortuosity and high porosity are constructed by incorporating the vertically aligned macro-channels from fir wood-derived carbon and the massive meso-and micro-channels created by KOH activation,which are beneficial for the diffusion of ions.The hydrophilic activated carbon nanotube/wood carbon electrode（ACNT/WC）exhibits an ultrahigh specific surface area of 1646.6 m²g^-1,a superior capacitance of 23995 m F cm^-2(493.7 F g^-1)and an excellent cycling stability with a capacitance retention of 98%after 10000 cycles at100 m A cm^-2.The assembled solid?state symmetric supercapacitor possesses a high areal power density of 15.7 m W cm^-2and a high areal energy density of 1.1 m Wh cm^-2.3.Hierarchically porous carbonized woods activated with KOH and ZnCl₂for solid-state supercapacitors:To further optimize the activation process and enhance the electrochemical performances,high-performance supercapacitors are assembled on the basis of double activated wood-derived carbon.An activated wood carbon（AWC）electrode is prepared by activating the wood carbon with KOH and ZnCl₂to create more mass transport paths and increase wettability.The hierarchically porous channels with low tortuosity and high porosity are beneficial for ion diffusion and energy storage.The hydrophilic AWC electrode exhibits an ultrahigh specific surface area of 1411.6 m²g^-1and a superior capacitance of 15394 m F cm^-2(316.7 F g^-1).The assembled solid?state symmetric supercapacitor exhibits a superior areal capacitance of 4888 m F cm^-2,a high volumetric energy density of 5.4 m Wh cm^-3,a high volumetric power density of 15.6 m W cm^-3and an excellent cycle stability of 98%capacitance retention over 1000 cycles at 10 m A cm^-2.