The Study On Electrodes Based On Polypyrrole For Supercapacitor

Supercapacitors?SCs,also known as electrochemical capacitors?are one kind of novel electrochemical energy storage devices.They possess higher energy density than traditional capacitors,and higher power density and longer cycle life than secondary batteries.Electrode materials have significant effects on the properties of SCs.Polypyrrole?PPy?,one of conducting polymers,has been extensively investigated due to its high electrical conductivity,easy preparation and chemical stability.Compared with chemical oxidation,PPy electrodes fabricated by electrochemical oxidation is a characteristic method to fabricate insulting binder-free electrodes by one-step preparation.However,few studies were carried out to investigate the effects of electropolymerization conditions on electrochemical capacitive properties of prepared PPy electrodes.In this paper,dopant,electropolymerization mode and parameter used in the process of electropolymerization PPy were optimized in detail,and core-shell polypyrrole/carbon nanotubes?PPy/CNTs?composite electrodes were prepared by electrochemical co-deposition.These studies have promoted the application of polypyrrole in SCs.The main contents of this paper are as follows:?1?The effects of different anionic dopants on the electrochemical capacitive properties of PPy electrodes were investigated.The component and morphology of prepared PPy electrodes were characterized by fourier transform infrared?FT-IR?,X-ray diffraction?XRD?,field emission scanning electron microscopy?SEM?and atomic force microscope?AFM?.Also,electrochemical properties tests were performed by cyclic voltammetry?CV?,galvanostatic charge and discharge?GCD?and electrochemical impedance spectroscopy?EIS?.Results show that the PPy-ClO₄ electrode prepared with lithium perchlorate as the dopant has the best electrochemical capacitive properties,which is related to its superior morphology and greater roughness.?2?A detailed study about the effects of different preparation conditions including electropolymerized mode,parameter,and current collector on the electrochemical capacitive performances of PPy electrodes was performed.FT-IR and XRD characterizations indicate the above preparation conditions have no effect on the component and crystal structure of PPy prepared.Electrochemical tests show the PPy electrode prepared using graphite foil as the current collector with high conductivity shows remarkably superior capacitive performances.SEM and AFM characterizations show galvanostatically polymerized PPy particles have obviously smaller aggregation degree and greater roughness than potentiostatically polymerized PPy particles,which results in better electrochemical properties for former.Thereinto,the PPy electrode prepared by galvanostatic mode with 2 mA cm^-2 shows the best electrochemical capacitive properties.?3?Core-shell PPy/CNTs composite electrodes have been prepared by facile electrochemical co-deposition.A detailed study regarding the effects of different preparation conditions including electrodeposition mode,parameter,current collector,and carboxylation degree of CNTs on the supercapacitive performances of PPy/CNTs electrodes is carried out.SEM characterizations show potentiostatically deposited PPy/CNTs present a compact two-dimensional morphology,while galvanostatically deposited PPy/CNTs have a favorable three-dimensional porous nano-network microstructure.Furthermore,the CNTs with higher carboxylation degree introduce more PPy,thereby resulting in better electrochemical performances.The optimized PPy/CNTs composite electrode shows a high specific capacitance of 185.3 mF cm^-2 at 0.5 mA cm^-2,superior rate capability,and outstanding cycling stability?retaining 88.5% of initial capacitance for 10,000 cycles?.