Preparation And Properties Of PPy-Based Supercapacitor Electrode Materials

The energy crisis and global warming have become two serious problems faced by mankind in the 21st century,and the energy revolution is inevitable,thus promoting the rapid development of the field of electrochemical energy storage.In electrochemical energy storage systems,batteries,conventional capacitors and supercapacitors are widely used.As a new type of energy storage device,supercapacitors have the advantages of high power density,green environmental protection and long cycle life,which have attracted the attention of scholars and have also been widely used in portable electronic products,hybrid vehicles and other fields..Electrode materials are the soul of supercapacitors and play an important role in the electrochemical performance of supercapacitors.Among them,polypyrrole（PPy）,as a kind of conductive polymer,has the advantages of simple synthesis process,good chemical stability,and non-toxicity.However,since PPy is usually accompanied by intercalation and intercalation of ions during the continuous charge-discharge process,resulting in a large volume change,which in turn affects its cycling stability,PPy lacks competitiveness in practical applications.Therefore,it is an effective way to compound PPy with suitable materials for structural control and to improve its volume change during charge and discharge,thereby enhancing its electrochemical performance.Ferric oxide（Fe₃O₄）has the advantages of high theoretical capacitance,wide working potential window,low cost,large natural storage capacity,simple and safe preparation and so on.In this paper,Fe₃O₄was introduced,and two kinds of Fe₃O₄/polypyrrole composite electrode materials with different structures and morphologies were prepared through fine structural design.The prepared samples were characterized by morphology and structure analysis,and the composite electrode materials were studied.The relationship between structural morphology and electrochemical performance.At the same time,a supercapacitor was assembled using the prepared composite electrode material,and its electrochemical performance was characterized to study its practical application potential.The main contents are as follows:（1）Fe₃O₄nanoparticles were prepared by solvothermal method.One-dimensional chain-like Fe₃O₄/PPy composites with core-shell structure were synthesized in aqueous hydrochloric acid by magnetically induced solution polymerization.By scanning electron microscopy（SEM）and transmission electron microscopy（TEM）for micromorphological analysis,it can be seen that the Fe₃O₄nanoparticles are relatively uniform in size and well dispersed,with an average size of about 168 nm.The Fe₃O₄/PPy composite electrode material is a controllable one-dimensional chain structure.In an environment similar to a uniform magnetic field created by two flat magnets,based on their own superparamagnetic properties,Fe₃O₄nanoparticles are specifically arranged along the direction of the magnetic field lines to form an unstable one-dimensional chain-like structure.Then,the polymer on the surface of Fe₃O₄nanoparticles was interconnected by solution polymerization,which further stabilized the structure.By adjusting the concentration of polymer monomers during polymerization,composite electrode materials with different chain formation degrees and polymer shell thicknesses can be obtained.The core-shell boundaries of Fe₃O₄/PPy composite electrode material can be clearly identified from the TEM images.In addition,the relative contents of the two components in the Fe₃O₄/PPy composite electrode material were analyzed by TGA curves.In the TGA curve of Fe₃O₄/PPy composite electrode material,the weight loss due to thermal decomposition of PPy is 69.69%.Therefore,the content of Fe₃O₄in this composite is about 30.31 wt%.Electrode materials were tested in a three-electrode system using an electrochemical workstation.The results show that the Fe₃O₄/PPy composite electrode material has high mass specific capacitance(697 F g^-1)and excellent rate capability.Furthermore,Fe₃O₄/PPy composite electrode material achieves a high energy density of 96.8Wh kg^-1at a power density of 500 W kg^-1.（2）A carbon cloth with good electrical conductivity was used as the current collector.Due to the strong hydrogen bonding between carbon cloth and Fe₃O₄,Fe₃O₄nanoparticles were directly anchored on the surface of carbon cloth by solvothermal method,and then PPy was slowly grown on its outer surface by electrochemical deposition technology to prepare CC-Fe₃O₄-PPy composite electrode material.The micromorphological characterization of the samples was carried out by SEM and TEM.The surface of each carbon fiber of the carbon cloth is smooth,indicating that the impurities on the carbon cloth have been removed after pretreatment.The carbon fibers are crisscrossed and intertwined to form a whole piece of carbon cloth.Compared with the smooth carbon fibers,Fe₃O₄particles grow uniformly on the surface of each carbon fiber in the precursor CC-Fe₃O₄,and the Fe₃O₄nanoparticles are about100 nm in size,which are tightly anchored on the surface of the carbon fibers.After the electrochemical deposition of PPy,PPy was coated on the surface of the precursor layer by layer,forming a thick PPy shell,and the lattice fringes belonging to Fe₃O₄also disappeared due to the coating of PPy.The electrochemical properties of the samples were analyzed,and the results showed that the specific capacitance of the CC-Fe₃O₄-PPy composite electrode material was about 3711 m F cm^-2when the current density was 1.0 m A cm^-2.Furthermore,the CC-Fe₃O₄-PPy composite electrode material exhibits excellent rate capability,with a capacitance retention rate of 94.3%even at a high current density of 10 m A cm^-2.At the same time,supercapacitors were prepared using CC-Fe₃O₄-PPy composite electrode material.The aqueous symmetric supercapacitor（SSC）can reach a power density of 0.22 m W cm^-2at an energy density of 69.87μWh cm^-2.The excellent electrochemical properties of the CC-Fe₃O₄-PPy composite electrode material reveal its great potential for application in high-performance supercapacitors.