Preparation Of Free-standing Porous Carbon-based Materials And Their Applications In All-solid-state Supercapacitors

Supercapacitors have received more and more attention in recent years due to their applications in the fields of fast charge and discharge and high power output.However,the performance of the most advanced supercapacitors is still insufficient for anticipated applications.Improving the energy density of supercapacitors is still a huge challenge.Developing electrode materials with excellent performance is the key to improving the performance of supercapacitors.Carbon materials have become a research hotspot in the field of supercapacitors due to their low price,wide sources,biodegradability,and high stability.In this study,a variety of carbon materials,including natural wood,carbon nanotubes（CNTs）,graphene oxide（GO）,and metal organic frameworks（MOFs）derived porous carbon were used as electrodes and assembled into all-solid supercapacitors.This article analyzes and discusses the morphology,chemical composition,structure,device construction method and electrochemical performance of the electrode.The specific content is as follows:（1）A simple,low-cost,and efficient method is used to synthesize all-solid-state symmetrical supercapacitor（SSC）ultra-thick electrodes based on self-supporting activated carbonized wood（AWC）.As an independent ultra-thick electrode,AWC has an area specific capacitance of 6.85F/cm² and 4.55 F/cm² at 1 m A/cm² and 20 m A/cm²,respectively,which shows excellent capacitance performance and rate performance.In addition,the SSC assembled by two AWC electrodes of approximately the same mass showed an excellent energy density of 0.23 Wh/cm²（4.59 Wh/Kg and 0.77 Wh/L）.Under the current density of 50 m A/cm²,the capacitance retention rate of SSC is as high as 86%after 10,000 cycles of charging and discharging,and it has good electrochemical stability.Its excellent electrochemical performance is related to the structural integrity of natural wood,the introduction of oxygen-containing functional groups,and the design of ultra-thick electrodes.（2）The activated carbonized wood composite metal organic framework derived nitrogen-doped porous material（AWC/C-ZIF-8）was prepared by in-situ growth of ZIF-8 nanoparticles on natural wood and high-temperature carbonization activation.The independent ultra thick electrode AWC/C-ZIF-8 has outstanding electrochemical performance.Exactly,the energy density is 1.73 Wh/cm²（36.45 Wh/Kg）at a power density of 500 m W/cm²（10.48 m W/kg）.At current densities of 1 m A/cm² and 50 m A/cm²,the area specific capacitance is 12.52 F/cm² and6.76 F/cm²,which shows excellent rate performance.At the current density of 50 m A/cm²,after10,000 cycles of charging and discharging,the capacitance retention rate is as high as 106%,which showing excellent cycle performance.The SSC composed of two AWC/C-ZIF-8electrodes of roughly the same mass has an energy density of 0.55 Wh/cm²（5.58 Wh/Kg）at a power density of 500 m W/cm²（5.1 m W/kg）.At the current density of 50 m A/cm²,after 10,000cycles of charging and discharging,the capacitance retention rate is as high as 96.8%,which shows good electrochemical stability.Three SSC charged to 1 V in series can light up 2.5 V,1W LED lights for about 30 minutes.（3）Mix the the aqueous solution of carbon nanotubes and orous graphene oxide in a certain proportion and filter the mixed liquor to a film.Then heat treatment at 350℃,N₂ atmosphere for 4 h,the graphene oxide is reduced to obtain reduced graphene oxide/carbon nanotube（CNTs/r GO）composite film electrode and used to prepare SSC.CNTs/r GO electrode has good flexibility,can be bent repeatedly and maintain the original appearance,while still showing good electrochemical performance.At the current density of 0.2 A/g,the mass specific capacitance is 205 F/g（area specific capacitance 189.6 m F/cm2）,and at the current density of5 A/g,the mass specific capacitance is 158 F/g（area specific capacitance 136.1 m F/cm²）.After10,000 cycles of charge and discharge at high current density,the capacitance retention rate is91%,which shows good cycle performance.The SSC prepared by the CNTs/r GO electrode has a mass specific capacitance of 42.28 F/g at a current density of 0.1 A/g.After 10,000 cycles of charging and discharging at a current density of 10 A/g,the capacitance retention rate was 86%.The SSC was tested for flexibility,and its electrochemical performance was only slightly attenuated when be bent at 135°.