Graphene And Its Composite Films As Electrodes Materials

Graphene has attracted much attention in fields such as physics, chemistry, and materials science, because of its unique properties and potential applications. Interest in graphene and graphene based composites used as electrodes for supercapacitors or transparent and conductive electrodes has been motivated by the need to develop functional energy storage devices and electronic devices. This work focuses on the synthesis of graphene and graphene base composite materials that were applied in electrodes for supercapacitors, and transparent and conductive electrodes.Free-standing, flexible and paper-like reduced graphene oxide (RGO) films were prepared by reducing graphene oxide (GO) films through different reduction processes, including HI, H2SO4, HI+H2SO4, NaOH, N2H4 and NaBH4 reduction process. The results reveal that HI reduction process is a more effective way to reduce GO and re-establish its molecular structure, and therefore improve the conductivity of RGO film. And it also maintain the shape and structure of the free-standing, flexible and paper-like RGO films. After reduced by H2SO4 and NaOH, the film is curl and become roll-like. After reduced by N2H4 and NaBH4, the film is broken because of the violent reaction process. Thus, the latter processes are not suitable for preparing free-standing RGO films.A facile one step co-reduction and low temperature solution process was developed to prepare RGO-Cu, RGO-Ag and RGO-Cu-Ag composite films on glass substrates. SEM and TEM micrographs reveal that Cu/Ag nanoparticles either distribute on the surface of RGO nanosheets or are covered by RGO. The conductivity and transparency of these films were studied. The results show that incorporation of Cu and Ag nanoparticles into graphene films can improve the conductivity of films. Ag nanoparticles are more effective in improving conductivity. The conductivity and transparency of composite films can be balanced through introducing optimized amount of Cu or Ag nanoparticles. The conductivity and transparency of RGO-Ag-Cu films with optimized metal nanoparticle concentration are as good as that of Ag-RGO composites. The RGO-Ag-Cu meets requirements of low cost, high conductivity and transparency, and could be a potential electrode material. The current low temperature solution process provides a new route to prepare transparent and conductive electrodes with low cost on various substrates, including glass and flexible polymer substrates.Free-standing microporous paper-like graphene films with electrodeposited polypyrrole (PPy) coatings were prepared. The microporous structures were produced by employing PS microspheres as sacrificial templates. PPy was coated on the films using a electrochemical deposition process to further improve the performance of these graphene electrode materials. The electrochemical performance of PPy coated microporous graphene films was evaluated and compared with solid graphene films. The results reveal that the incorporation of PPy and microporous structures significantly improve the electrochemical performance of graphene based electrodes for supercapacitors. Microporous films have higher capacitance than their solid counterparts although they have slightly lower conductivity, which reveals that microporous structures play an important role in the electrochemical performance of the electrode materials. The PPy coated microporous graphene films has better electrochemical performance than uncoated counterparts, which indicates that PPy coatings have significant effects on graphene based electrodes. This in-depth research on free-standing microporous paper-like graphene with electrodeposited PPy coatings provides a new route to combine the advantages of both graphene and PPy so as to produce high performance electrodes for supercapactitors.Flexible, free-standing TiO2-graphene-PPy composite films as electrodes for supercapacitors were prepared, which harness the advantage of both PPy and TiO2. Firstly, titania precursor and graphene oxide (GO) composite films were prepared by directly mixing and drying strategy. Secondly, the hydriodic acid (HI) reduction process were employed to reduce GO to obtain graphene/titania precursor composite films. Thirdly, heat treatments at different temperature (400,500 and 600 ℃) were carried out to obtain TiO2-G composite films with different titania crystalline phase. Finally, PPy was deposited on the surface of the as-prepared TiO2-G to form three-phase composite films. The introduction of TiO2 remarkably improves the pesudocapacitance and electrochemical stability of G based electrodes. The highest capacitance was obtained with the TiO2 content of 14.6%. The PPy coating also improves the capacitance of G-PPy composite electrodes. The role of PPy lies more in the improvement of conductivity, which increases the current density of electrodes under working condition. However, the introduction of PPy decreases the electrochemical stability of composite electrodes. The extremely high capacitance and good electrochemical stability of TiO2-G-PPy composite electrodes reveals that there are synergistic effects of TiO2 and PPy on the composites. Different TiO2 phase does not have remarkable effects on capacitance of TiO2-G system. After coated with PPy, different TiO2 phases exhibit different behaviors. Anatase-G-PPy has high capacitance whereas rutile-G-PPy has good stability. TiO2-G-PPy heat-treated at 500 ℃ has the mixed TiO2 phases, and therefore has both high capacitance and good stability.