Preparation And Electrochemical Properties Of Graphene/Pseudo-capacitance Materials Composite

Nowadays，due to environmental issues and depleting fossil fuels, the increasing demandfor renewable energy sources has stimulated intense research on energy storage andconversion from alternative energy sources. Supercapacitors （SCs）, as charge-storage devicesexhibiting high-power density, excellent reversibility and cycle-ability, are considered aspromising candidates for energy storage. Energy can be stored in supercapacitors by means ofeither ion adsorption at the electrode/electrolyte interface （namely, electrical double-layercapacitors, EDLCs） or fast and reversible faradic reactions （namely, pseudocapacitors）. Todate, carbon materials, transition metal oxides and conducting polymers have been identifiedas the most promising materials for SCs. However, each material has its unique advantagesand disadvantages for SC application. For example, carbon materials have outstandingelectrical properties, long life-cycles and beneficial mechanical properties, but low specificcapacitance. Transition metal oxides and conducting polymers have relatively highercapacitance and fast redox kinetics, while the relatively low mechanical stability and cyclelife limits its application for SCs. The challenge for this studies is the synthesis of binarycomposites of carbon material GNS, conducting polymers and metal oxides as materials forsupercapacitors, is to effectively utilize their benefits while overcoming their disadvantages.Reduced graphene nanosheet/urchin-like MnO₂（GNS/MnO₂） composite for asupercapacitor electrode has been fabricated by a mild hydrothermal route. Followinginvestigation by scanning electron microscopy （SEM） and transmission electron microscopy（TEM）, we propose an in situ formation of MnO₂nanoparticles onto graphene nanosheets.The unique structure greatly increases specific surface area of the composite and theutilization of MnO₂. The electrochemical performance of the electrode is analyzed by cyclicvoltammetry, electrochemical impedance spectrometry and chronopotentiometry. Resultsshow that the GNS/MnO₂composite exhibits a maximum specific capacitance of263F/g andan excellent cycle life with capacity retention of about99%after500cycles. The methodprovides a facile and straightforward approach to deposit MnO₂nanoparticles onto graphenesheets; it could be readily extended to the preparation of other classes of hybrids based onGNS sheets for technological application.A novel layer-by-layer composite film is developed by a template-free approach combining the nanostructured conductive polymer polyaniline with highly electrically conductivegraphene nanosheets in a multilayered configuration. The in situ polymerization of anilinemonomer on the surface of GNS nanosheets can provide larger surface area to interface withions and electrons. The GNS/PANI products show a sandwich structure which significantlyimproved the mechanical properties and flexibility of the composite. And the GNS/PANIcomposite electrodes exhibit high specific capacitance and improved cycling stability inelectrochemical tests, indicating improved networks for electrochemical energy applications.A novel nanoarchitecture is developed by combining the nanostructure Fe₂O₃with highlyelectrically conductive graphene nanosheets to achieve high specific capacitance and lowelectronic resistance for supercapacitor electrode applications. The obtained graphene/Fe2O3composites formed a uniform nanocomposite with the F₂O₃nanorods absorbed on thegraphene surface and/or filled between the graphene sheets. The electrochemicalperformances of the hybrid GNS/Fe₂O₃supercapacitor were tested in6M KOH electrolyte.This composite electrode exhibits high specific capacitance of320F/g at10mA/cm²and anexcellent cycle-ability with capacity retention of about90%after500cycles. A simple andcost-effective preparation technique of graphene and its nanocomposites with good capacitivebehavior encourages its commercial use.