Fabrication Of Flexible Electrode Based On Bacterial Cellulose And Its Application In Supercapacitors

Flexible energy-storage devices are attracting increasing attention as they show unique promising advantages,such as flexibility,shape diversity,light weight,and so on;these properties enable applications in portable,flexible,and even wearable electronic devices.Among the options,supercapacitors,commonly referred to as electrochemical capacitors,are widely recognized as a potential energy storage system due to their high power,fast charge/discharge rate,long cycling life-time,and low cost.Apparently,the key challenges in achieving flexible energy-storage devices are the selection and design of bendable current collectors with good mechanical properties and the fabrication of flexible electrode materials with a high capacity and excellent conductivity.As industrially produced cheap biomass materials,bacterial cellulose(BC)has a 3D interconnected nanofibrous network structure consisting of a randomly assemble nanofibers with widths of 20-100 nm and plentiful surface hydroxyl groups,and thus provides sufficient specific surface area,extensive porosity and high tensile strength.Given these merits,BC endows the flexible electrode with great hydrophilicity and high mass loading when used as supported substrate.In this paper,two kinds of free-standing flexible paper electrodes with large mass loading,high specific areal capacitance and excellent mechanical properties were prepared by facile and low-cost method and then we investigated the electrochemical performance of these electrodes.Polypyrrole(PPy),as a kind of conducting polymer,has been demonstrated to be a promising pseudocapacitive electrode material for flexible supercapacitors.Competitive advantages of the PPy include high electrical conductivity,facile synthesis,low cost and good environmental stability.However,direct use of PPy as the flexible electrode material will seriously impede their utilization for its poor mechanical properties.Hereby,we report on a freestanding conductive electrode was fabricated by electrochemically polymerizing thin polypyrrole film on graphene/carbon nanotube/bacterial cellulose(GN/CNT/BC)electrode.Comparing with chemical synthesis methods,the PPy prepared by electrochemical polymerization will be directly grown and attached on the electrode surface,which allows direct control of the PPy mass and structure.Furthermore,the effect of dopant concentration and loading mass on electrode performance were systematically investigated.The as-obtained PPy/GN/CNT/BC electrode exhibits good areal capacitance of 811.4 mF cm-2 and 1191 m F cm-2 in Na2SO4 and H2SO4 electrolyte,respectively.As for N-ASPC/GN/BC,the abundant biomass waste(shaddock peel)is selected as carbon precursor.Benefit from its strong solution absorption capacity and inherent structure,we developed a template-free and smart strategy to prepare N-doped porous carbon with a high specific surface area and porosity by two simple steps consisting of a doping process and then a further activation.Despite of high mass loading(8 mg cm-2),this paper electrode remains ultrahigh mechanical tensile strength and good electrical conductivity reaching 32 MPa and 1550 S m-1.When evaluated in three-electrode system,the N-ASPC/GN/BC electrode delivers an excellent areal capacitance up to 2004 m F cm-2(250.5 F g-1)in 6 mol L-1 KOH.