Preparation Of Polypyrrole Based Composite Electrodes And Study Of Electrochemical Capacitive Properties

Supercapacitors（SC）,also known as electrochemical capacitors,have a greater energy density than traditional dielectric capacitors,and a higher power density and a longer cycle life than batteries,have aroused researchers’great interest in research.As a conductive polymer,polypyrrole（PPy）has been widely studied as an electrode material for supercapacitors due to its advantages of high conductivity,easy synthesis,low cost and environmental friendliness.However,there are two main shortcomings in the supercapacitor electrode based on PPy.First,it has the characteristic of dense growth,which is not conducive to electrolyte entering into the interior of the electroactive material.Second,PPy’s circulative stability is poor,which is mainly due to the doping/dedoping of ions leading to its volume expansion and contraction caused by.In addition,in addition to the problems of PPy electroactive materials themselves,current collector is also an important factor affecting the electrochemical capacitance performance of the constructed electrode.However,at present,few studies have improved the electrochemical performance of the electrode from the perspective of current collector.Based on the above problems,this study improves the electrochemical capacitance performance of PPy electrodes by constructing composite electrode materials and improving the current collector,which promotes the application of PPy electrode materials in the field of electrochemical energy storage.The main contents of this paper are as follows:（1）With graphite paper（GP）as the current collector,the core-shell multi-wall carbon nanotube@polypyrrole（GP/MWCNT@PPy）composite electrode was prepared by electrochemical co-deposition method.Compared with the GP/PPy electrode,it shows a significantly improved electrochemical capacitance performance.This can be attributed to the core-shell three-dimensional porous network structure formed by the input of MWCNT with excellent electrical conductivity,which promotes the scattered growth of PPy and significantly improves its electrical active surface area.Further,this study also proposes a simple and feasible mechanical stripping method to roughen the GP current collector,and the obtained mechanical stripping graphite paper（MEGP）current collector shows a unique layered microstructure.Electrochemical test results show that the MEGP/MWCNT@PPy electrode has significantly improved electrochemical performance than the GP/MWCNT@PPy electrode,which can be attributed to the more convenient charge transmission channel between the roughed current collector and the electrically active material.Symmetrical flexible solid-state SC assembled with MEGP/MWCNT@PPy electrodes show an area capacitance of 101.5 m F cm^-2under the current density of 0.5 m A cm^-2.After 10,000 cycles,87.1%of the initial capacitance value is retained,indicating that its the high electrochemical cycle stability maintains.95.1%of the initial capacitance after 400 mechanical deformations,showing excellent mechanical stability.（2）PPy/MnO₂ composite electrode was prepared by electrochemical polymerisation,and the composition and morphology of the electrode material were characterised by X-ray diffraction,infrared spectroscopy and scanning electron microscope.Compared with the electrochemical capacitance performance of PPy electrode,the electrochemical test results show that the electrochemical performance of PPy electrode is significantly improved by MnO₂.At the sweeping speed of 10 m V s^-1,the area capacitance of the PPy electrode rises from 142.0 m F cm^-2to 170.9 m F cm^-2.Symmetrical solid-state SC are further constructed through the PPy/MnO₂electrode.At 1 m A cm^-2,it shows an area capacitance of 84.5 m F cm^-2.When the GCD current density increases from 1 to 5 m A cm^-2,87.4%of the initial capacitance is retained.After 2,500 rounds of CV cycle,93.0%of the initial capacitance is retained.The improvement of PPy electrochemical properties may be attributed to the addition of the incorporated MnO₂,which leads to the more looser structure of PPy and the synergy between them.In addition,MnO₂also provides mechanical support for the volume expansion and contraction of PPy.