Capacitive Properties Of Flexible Polypyrrole/Carbon Fibers In Various Electrolyte

Supercapacitor?SC?,a new emerged energy storage device,has attracted tremendous attention because of its high power densities,high charge-discharge efficiency and excellent cycling stability.At present,the demands for high-performance power sources in flexible personal electronics and wearable electronics have been boosting the requirements for inexpensive,flexible and light-weight energy storage systems with high energy and power density.It is proved that the performance of the SCs is strongly affected by the materials of electrode,electrolytes,separators and so on.Therefore,besides the electrode materials,the electrolyte in the SCs shall be chosen carefully in order to improve the performance of SCs.Graphene,a single-atom-thick sheet constructed by hexagonally arrayed sp2-bonded carbon atoms has recently attracted a great deal of attention.The rGO sheets have limited solubility in water because the existed high cohesive Van der Waals energy that adheres graphitic sheets together.The low solubility has restricted rGO's applications in many fields.Therefore,it is important to develope a simple and environmental method to synthetize rGO with high solubility.?1?Polypyrrole?PPy?doped with large counter anion of dodecyl benzene sulfonate?DBS?has been electrodeposited on carbon fibers to obtain the composite of PPy/DBS/CFs.The microstructures of PPy/DBS/CFs composites are observed by scanning electron microscope?SEM?,and the electrochemical properties of the composites are investigated by using electrochemical techniques.The flexible wire-shaped supercapacitors can be fabricated conveniently and the performances of the flexible capacitors are evaluated by cyclic voltammetry?CV?,galvanostatic charge/discharge?GCD?and electrochemical impedance spectroscopy?EIS?methods in different polyvinyl alcohol?PVA?-based gel electrolytes.The results show that the electrolytes have significant influence on the SCs' performances.The specific capacitance of PPy/DBS/CF can reach to about 29.0 mF cm^-1 when LiCl/PVA is used as electrolyte.The energy density and power density of the capacitors based on LiCl/PVA electrolyte can get 1.20 mWh cm-3 and 0.59 W cm-3 at discharge current density of 1.50 A cm-3.Furthermore,the flexible capacitors based on LiCl/PVA electrolyte have excellent cyclic stability,which can retain 90.5%of the initial capacitance after 5000 cycles.?2?A simple electrochemical deposition method is used to synthesize PPy doped with counter ion of chloridion?Cl-?on carbon fibers.The as-prepared PPy/Cl/CFs electrode materials are characterized using SEM.The anion content in PPy at oxidized and reduced states in different electrolytes is detected by X-ray photoelectron spectroscopy?XPS?and the electrochemical properties of the SCs assembled by PPy/C]/CFs electrode materials are investigated by CV,GCD and EIS.The flexible capacitors can be fabricated conveniently in five different PVA gel electrolytes.The results show that the specific capacitance of capacitor of PPy/Cl/CFs based on H3PO4 gel electrolytes is about 41.6 mF cm^-1 at current density of 0.1 mA cm^-1 and can retain 91.5%of their initial capacitance after 15000 cycles,which is much better than in other gel electrolytes.?3?One-pot approach is presented to synthesize sulfonated reduced graphene oxide?S-rGO?by using L-ascorbic acid?L-AA?and aryl diazonium salt of sulfanilic acid.The preparation conditions have been optimized in order to obtain isolated and conductive S-rGO,and the products have been characterized by Ultraviolet-Visible spectroscopy,Fourier transformed infrared spectroscopy,Raman,XPS and X-ray powder diffraction and electrochemical methods.The results show that the S-rGO sheets possess excellent water-solubility and high electrical conductivity.The optimum S-rGO exhibits a specific capacitance of 205 F g^-1 and good cycling stability?3.9%decreasing after 10000 cycles?.