| The pH effect on electro-polymerization of aniline (An) and the morphologies and pseudo-capacitive properties of the resulting polyaniline (PANI) were investigated systematically in this thesis. Chemical anchoring of modified nickel oxide nanoparticles onto PANI chains was conducted through electro-co-polymerization of aniline and N-substituted aniline grafted on surfaces of nickel oxide nanoparticles, and the morphologies and pseudo-capacitive properties of the resulting composite film were also investigated. Highly conductive graphene was produced through reducing graphene oxide (GO) under constant potential. Symmetric model supercapacitors were constructed using graphene films as electrodes. Electrochemical and pseudo-capacitive properties of the films and supercapacitors were studied by cyclic voltammetry and constant current charging-discharging experiments.The pH effect on electro-polymerizition of An on carbon cloth substrate was investigated through cyclic voltammetries in0.1mol·L-1An solution with pH=0～14.0(0.1mol·L-1KNO3as supporting electrolyte). The resulting PANI films were characterized by FT-IR and Scanning Electron Microscopy (SEM). The PANI electrodeposited at pH1.0exhibited interconnected network of nanofibres. Upon increasing the pH of the electro-polymerization media, surface active sites for secondary growth began to appear on the nanofibers. The PANI nanofibres started to intertangle with each other to form granule morphologies when the pH of the electro-polymerization media increased to5.0. PANI films obtained at pH>6.0exhibited similar granular morphology. The electrochemical pseudo-capacitive properties of PANI in0.5mol·L-1H2SO4and1.0mol·L-1NaNO3(pH=1.0) were studied through constant current charge-discharge, at1.0～7.0mA/cm2between0～0.65V. PANI films obtained at pH0～1.0and5.0～13.0showed good electrochemical pseudocapacitive properties in both0.5mol·L-1H2SO4and1.0mol·L-1NaNO3(pH=1.0) solutions. The specific capacitance of the PANI obtained at pH=12.0in0.5mol·L-1H2SO4and1.0mol·L-1NaNO3(pH=1.0) solution at1.0mA/cm2are497and450F/g, respectively.Nickel oxide (NiO) nano-particles with diameter of ca.10nm were synthesized by calcination at300℃of its precursor Ni2(OH)2CO3, which was synthesized through precipitation process in mixed solvents of distilled water and ethanol (V:V=1:1). NiO nanopartices were modified by silane coupling agent containing aniline moieties. The grafting of N-substituted aniline on surfaces of NiO nanoparticles were conducted through hydrolysis of triethoxysilylmethyl N-substituted aniline (ND-42) and the following condensation reaction with silanol groups on surfaces of NiO. Chemical anchoring of modified NiO nanoparticles onto PANI chains was conducted through electro-co-polymerization of aniline and N-substituted aniline grafted on surfaces of NiO nanoparticles through cyclic voltammetry in solution containing0.1mol·L-1An,0.4g·L-1ND42-NiO,0.1mol·L-1KNO3and0.5mol·L-1H2SO4over potential window of-0.3to1.2V vs. SCE at scan rate of25mV/s. The electrochemical pseudo-capacitive properties of the composite film PANI/ND42-NiO in0.5mol·L-1H2SO4and1.0mol·L-1NaNO3(pH=1.0) were studied through constant current charge-discharge at1.0～7.0mA/cm2between0～0.65V. PANI/ND42-NiO exhibited a specific capacitance17%higher than that of PANI.Graphene oxide (GO) with different oxidation levels (GO1, GO2, and GO3) were prepared from ground graphite flakes by controlling oxidizing time based on Hummers’s method. The effects of oxidation levels on GO and resulting graphene were investigated through UV-vis, FT-IR, Raman, cyclic voltammetry, SEM, AFM and contact angle testing. GO3solutions were electrochemically reduced at-1.7V, and the resulting material were characterized through UV-vis, FT-IR, Raman, and cyclic voltammetry. By in-situ electrochemical reducing GO3/Au-PET, ERG3/Au-PET was obtained. This electrochemical synthetic technique offers much more control over reaction parameters such as the applied voltage, electrical current and reaction time. In addition, the film size and thickness can be pre-determined by controlling the deposition of the precursor GO film on the electrode surface. The effects of reducing voltage and pH of the reaction media on the resulting ERG3/Au-PET were investigated through Raman, SEM and cyclic voltammetry etc. It was found that GO3could be reduced adequately at-1.1V in0.5mol·L-1NaNO3electrolyte. Chemical reduction method produced graphene film (CRG3/Au-PET)4times more resistive than ERG3/Au-PET; giving an average resistance (n=3) of293Ω/square for CRG3/Au-PET and65.7Ω/square for ERG3/Au-PET respectively measured across a～50μm gap. This might be due to the better electronic alignment of the resulting ERG3structure under the influence of the applied voltage during reduction.Electrochemical capacitive properties of ERG3/Au-PET and ERG3/Au-PVDF were investigated in1.0mol·L-1NaNO3,1.0mol·L-1H2SO4, and5.0mol·L-1KOH solutions through cyclic votammetry and constant current charge-discharge. ERG/Au-PET exhibited specific capacitance of2101.44F/g,761.9F/g and735.5F/g in NaNO3, H2SO4and KOH, respectively. Electrochemical symmetrical supercapacitors based on ERG3/Au-PET with1.0mol·L-1NaNO3as electrolyte achieved a maximum specific capacitance of1508.13F/g with energy density of0.838kWh/kg at power density of424.33kW/kg. The capacitance remained at80%of the original value after500charge-discharge cycles. These promising results illustrate the great potential of this ERGO film in applications such as green electrical energy storage devices under environmentally friendly neutral aqueous solution conditions. Electrochemical symmetrical supercapacitors based on ERG3/Au-PVDF with1.0mol·L-1NaNO3as electrolyte achieved a maximum specific capacitance of594.1F/g. The capacitance of the supercapacitors with NaNO3, H2SO4and KOH as electrolytes remained80.0%,79.5%and79.4%respectively of the original value after1000charging-discharging cycles. These promising results illustrate the great potential of ERG3/Au-PVDF in electrical energy storage devices under different pH environments. |
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