Synthesis And Electrochemical Characterizations Of Metal Oxide And Carbon Based Nanomaterials For High Performance Negative Electrode Of Supercapacitor

Supercapacitors?SCs?have received considerable attention owing to their unique characteristics because of their long life span,low cost,excellent rate capability and high power densities.However,low energy densities of SCs limited their practical applications due to the lack of high-performance negative electrode materials.The charge storage properties of the SCs can be enhanced by taking the advantage of different nanostructured and carbon based electrode materials with stable crystal structure.These negative supercapacitor electrode materials possesses high surface area,more electroactive sites and shorter electrolyte diffusion lengths.This thesis work focus on the synthesis and enhanced electrochemical performance of metal oxide and carbon based negative electrode materials.Firstly,a simple,low-cost one-step hydrothermal method was successfully used to prepare?-Fe₂O₃hollow nanospheres.The formation of?-Fe₂O₃-HNS was confirmed by scanning and transmission electron microscopy and further characterized by XRD,FTIR and other microstructure and spectroscopic techniques.To investigate the electrochemical properties of?-Fe₂O₃-HNS,we systemically tested it in a basic potassium hydroxide?KOH?electrolyte under the extended negative potential window of?-1.2-0.0V?versus Ag/Ag Cl.Among three samples of?-Fe₂O₃nanospheres,the?-Fe₂O₃-HNS sample manifests a record high specific capacitance of 1041.18 F/g while,partially hollow and solid?-Fe₂O₃nanospheres displayed relatively low specific capacitances of 534.31 and 325.38 F/g at 1 A/g at identical conditions,respectively.The?-Fe₂O₃-HNS sample demonstrates excellent cycling retention of 98.88%,while partially hollow and solid?-Fe₂O₃nanospheres samples retained94.23%and 88.25%,respectively at a high current density of 15 A/g after 10000charge/discharge cycles.Furthermore,we investigated the quantification of capacitive and diffusion controlled stored charge for high performance charge storage kinetics of as-prepared electrodes,by employing power's law and impressively?-Fe₂O₃-HNS sample reveals high capacitive type storage of 85%at 10 m V/s.The obtainable results fully exhibit the unique advantage of a hollow structure to fabricate superior-performance negative electrode materials for supercapacitors.Secondly,the iron oxide nanoparticles?Fe₃O₄-NPs?were surface-modified by polyaniline?PANI?coating using a simple hydrothermal method.The formation of polyaniline-coated iron oxide nanoparticles?Fe₃O₄/PANI-NPs?were confirmed by scanning and transmission electron microscopy and further characterized by XRD,FTIR and other microstructure and spectroscopic techniques.The performance of Fe₃O₄-NPs and Fe₃O₄/PANI-NPs as anode materials for supercapacitors in alkaline potassium hydroxide?KOH?electrolyte was studied.The Fe₃O₄/PANI-NPs sample possesses specific capacitance of 1669.18 F/g,while Fe₃O₄-NPs exhibit 1351.13 F/g at 1 A/g at identical conditions.The Fe₃O₄/PANI-NPs sample exhibits remarkable electrochemical cycling performance?96.5%?over pristine Fe₃O₄-NPs?92%?at high current density of 15 A/g by exceeding the 25000times charge/discharge cycles.Furthermore,we analyzed the charge storage contributions by implementing the power's law and interestingly Fe₃O₄/PANI-NPs sample exhibits high capacitive type storage(85%at 10 m Vs^-1).Based on our experiments,Fe₃O₄/PANI-NPs shows exceptional high electrochemical results in basic electrolyte with excellent stability and surpass most of recently reported work based on the iron oxides and their composites.Therefore,the proposed strategy can be applied to fabricate the high-performance negative electrode materials for supercapacitors.Thirdly,iron oxide?Fe₃O₄?and reduced graphene oxide?r GO?nano-disc composites?Fe₃O₄/r GO?were prepared by hydrothermal process.The morphology and structure of Fe₃O₄/r GO composites were analyzed using various characterization methods.When Fe₃O₄/r GO composite is tested as a negative electrode in basic potassium hydroxide?KOH?electrolyte using three-electrode system,r GO was found to greatly enhance the performance of Fe₃O₄/r GO composite as negative electrode.Compared with Fe₃O₄ nanodiscs,Fe₃O₄/r GO composites showed a significantly higher specific capacitance of 1149 F/g at 1.5 A/g,while Fe₃O₄ nanodiscs were 919.2 F/g.In addition,Fe₃O₄/r GO composites showed an excellent cycling stability of 97.53%after running 10000 GCD cycles at a current density of 10 A/g,while,Fe₃O₄ was only 87.82%at identical conditions.The fascinating electrochemical performance can be benefited for future fabrications of iron graphene-based negative electrode material for SCs.Fourthly,the synthesis of a novel ternary Fe₃O₄-r GO-Mo O₃ nanocomposite?FGM?was established by utilizing the fast and facile microwave hydrothermal process.The optimized composition of FGM nanocomposite is characterized by the XPS,EDS,Raman,SEM,TEM and HRTEM techniques.The FGM-NPs supported on the carbon cloth?FGM@CC?electrode is used to investigate the electrochemical charge storage properties in basic potassium hydroxide?KOH?electrolyte.The charge storage properties of the FGM@CC electrode were studied by the CV,GCD and EIS techniques.The obtained results of FGM@CC electrode in aqueous electrolyte showed excellent electrochemical performance as compared with single metal oxides:maximum specific capacitance of 1666.50 F/g?FGM@CC?,1075.26 F/g?Fe₃O₄NPs?and 952.38 F/g?Mo O₃-NPs?at a current density of 2.5 A/g.The capacitance retention was 95.01%?FGM@CC?,94.1%?Fe₃O₄-NPs?and 92.5%?Mo O₃-NPs?after 5000 cycles.Further,the charge storage mechanism is analyzed in the light of power's law and systematical investigated the capacitive and diffusion controlled based stored charge in FGM@CC electrode.Thus FGM nanocomposite showed best performance as the anode material for the next generation supercapacitors.Fifthly,the mesoporous C₆₀-fullerene micro-particles?m CF?were prepared using Kr?tschmer-Huffman method,followed by solvent extraction and column chromatography for purification.The m CF supported on carbon cloth?m CF@CC?is used as the electrode to study charge storage properties.The m CF@CC exhibits excellent capacitance of 440 F/g at 2 A/g,good rate capability of 84.85%at high current density of 12 A/g and stable life up to 10000cycles.Additionally,the m CF@CC electrode possesses good flexible characteristics and presents almost same performance after 1000 bending cycles.Thus,mesoporous C₆₀-fullerene micro-particles can be employed as negative electrode material for the flexible next generation supercapacitors.Additionally,the porous Ce O₂-NPs were prepared via precipitation and the hydrothermal processing.The XRD and FTIR confirmed that Ce O₂-NPs prepared by our synthesis method do not contain any commonly present hydroxide related impurities.The charge storage properties of Ce O₂-NPs supported on carbon cloth?Ce O₂-NPs@CC?showed excellent electrochemical performance(C_sp=877.5 F/g at 3 A/g)with excellent cycling stability of 96.52%at 20 A/g after 5000 cycles.Surprisingly Ce O₂-NPs@CC electrode exhibits outstanding 79.77%rate capability at 6-fold high current-density.The high energy storage performance of Ce O₂-NPs@CC electrode attributed to the rich redox chemistry and porous structure of Ce O₂.Overall,in this work,based on the proposed synthesis methods,and performance exploration of metal oxide and carbon based nanomaterials,the adsorption/desorption of electrolyte ions to the electrode surface was enhanced on the carbon cloth substrate.The hollow nanostructures,r GO,PANI type conductive matrix wrapped on nanomaterials,Ce O₂-NPs and carbon based nanomaterials were also developed and prepared which showed excellent electrochemical performance as negative electrode materials of supercapacitors.We believe that the present results of six different work have shown a significant effect towards a new way of synthesis and fabrication of highly efficient and stable negative SCs electrode materials to promote their practical applications.