Preparation Of Metal Oxides/graphene Based Composites And Their Application In Energy Conversion And Storage

In the past decade,interests about the exploitation of new energy have been growing due to concerns over energy crisis and global wanning related to the burning of fossil fuels,including conversion,utilization and storage of new energy.Among some promising energies,solar energy featuring sustainable,stable,inexpensive and environment-friendly has received much more attention.Dye-sensitized solar cells（DSSCs）have become the representative as an alternative to conventional silicon-based and thin-film solar cells.In the utilization of solar energy,many researchers focus on exploring various solar energy conversion photocatalysts to degrade pollutants.Meanwhile,among various devices storing energy,due to high power capability,long-term cycle life and fast charge-discharge procedures,supercapacitors have been paid great interest as alternatives to energy storage systems.In this paper,based on SnO₂,NiCo2O4,Co3O4 nanomaterials and them with RGO nanocomposites,we investigate the counter electrode in DSSCs,photocatalysts and electrode materials for supercapacitors.This paper contains fourth chapters.The first chapter mainly presents the current research situation of DSSCs,photocatalytic degradation and supercapacitors.Then we give the idea and significance of the paper.In the second chapter,SnO₂ quantum dots anchored on RGO（SnO₂@RGO）and TiO₂ nanospheres（TiO₂/SnO₂ composites）have been used as the counter electrode in DSSCs and the photocatalyst in degradation of methyl orange,respectivly.We first prepare the the SnO₂ nanoparticle with RGO.In all tests,nanocomposite has huge performance increases compared with the pure samples,including electrochemical impedance spectra,Tafel curves,cyclic voltammetry and photovoltaic efficiency.It means that SnO₂@RGO nanocomposite will be an alternative to Pt as a counter-electrode.TiO₂/SnO₂ composites have been synthesized via a simple one-step hydrothermal approach.A mass of SnO₂ quantum dots dis-perse onto the surface of TiO₂ nanospheres evenly and arranged uniformly andorderly.The synergistic effect of the unique structure makes the composites have better UV light absorption.In the third chapter,nanohybrids of porous Co3O4 nanosheets with RGO were synthesized via a facile hydrothermal reduction process.Then the composite was used as CEs in DSSCs and electrodes in supercapacitors.The nanocomposite avoids the disadvantages of Co3O4 morphology,in this way both of their advantages are developed.Compared with the pure porous Co3O4 nanosheets,the nanohybrids have a larger specific surface area,which not only help in the electrolyte adsorption but also offer more electrocatalytic active sites.Meanwhile,considering the characteristics of 2D porous Co3O4 nanosheets anchored on RGO nanosheets,the nanocomposite was endowed the excellent electrochemical performance.The specific capacitance of Co3O4@RGO is almost three times as much as that of the pure Co3O4.Both electrodes demonstrated excellent long cycle life during 3000 cycles.In the fourth chapter,we try to use the multiple oxide compounds as the counter electrode and investigate the effect of performance by exploring the controllable synthesis of microstructure.Firstly,we mainly focus on the synthesizing NiCo2O4 nanobelts and the nanocomposite of NiCo2O4 nanobelts with RGO.The as-obtained nanocomposite has huge performance increases in all respects.In which,cycle stability has the most obvious ascension.By compared the morphology,the unique nanocomposite microstructure is the key to performance improvement.Meanwhile,the synergistic effect of the RGO and NiCo2O4 nanobelts make the system to achieve their full potential.This chapter gives a good thinking to gain a performance boost.Then,NiCo2O4 nanosheets,nanorods and nanoflowers have been synthesized by the thermal treatment of the three individual precursors which were prepared via three different hydrothermal processes.Due to the unique structure characteristics;the DSSCs equipped with NiCo2O4 nanoflowers CE achieved the highest PCE.Meanwhile,for better understanding of the formation of the porous NiCo2O4 nanoflowers,time-dependent experiments were carried out by fabricating samples at different hydrothermal reaction time.