3D Silk Fibroin/Carbon Nanotube Array Composite Matrix For Flexible Solid-state Supercapacitors

With the diversification of the new generation of electronic devices,flexible solid-state supercapacitor(FSCs)energy storage devices with the advantages of light weight,portability and environmental friendliness have attracted extensive attention from researchers.Porous conductive carbon-based materials such as porous carbon,graphene,carbon nanotubes are common electrode materials for supercapacitors.Among them,vertically oriented carbon nanotubes array(CNTA)is considered to be an ideal choice for supercapacitor electrode materials due to its high specific surface area,regular pore structure and short ion transfer path.However,CNTA has so poor mechanical strength that it easily collapses or cracks.Meanwhile,due to its super-hydrophobicity,the traditional electrolyte aqueous solution is difficult to permeate,which seriously hinders its application in flexible energy storage devices.In this paper,a 3D porous conducting scaffold was prepared by using a vertically oriented CNTA modified with silk fibroin(SF).The SF scaffold can effectively improve the mechanical strength and hydrophilicity of CNTA@SF composite material.Additionally the pyridine-type nitrogen generated by carbonization can further improve the electrochemical performance of the device while maintaining the flexibility and hydrophilicity of the original device.Finally,the charge transfer resistance(Rct)of the CNTA@C device is reduced by about 40%and the volumetric capacitance is increased by 60%.In order to improve the energy density,we further introduced Fe3+to prepare redox-enhanced FSCs devices.After preparing and comparing three different mixed gel electrolyte systems,we find that Fe3+ @PVA-H2SO4@CNTA system had the highest specific capacitance and energy density.However,the serious self-discharge and redox shuttle effect lead to the poor cyclic stability of the device.Next,we adopted SF@CNTA support,which can effectively fix Fe3+ by the columbic attraction of SF.As a result,the shuttle effect and irreversible redox reaction is greatly inhibited and the device's cyclic stability gets dramatically enhanced(the capacitance gets almost no loss after 10000 cycles).Meanwhile,FSC device exhibits the ultra-high area specific capacitance(999 mF/cm2)and energy density(0.089 mWh/cm2(0.34 mWh/cm3)).This experimental result provides a new idea for the design and preparation of other redox-enhanced supercapacitors.In summary,we have successfully designed a 3D supercapacitor device based on carbon nanotube array and silk fibroin(SF),which has a good application prospect on biocompatible FSCs devices and implantable electronic devices.