Preparation And Electrochemistry Performance Study Of Conducting Polymers Modified Activate Carbon Electrodes

Electrochemical supercapacitor is a new energy storage equipment between batteries and electrostatic capacitors. It has unique applied advantage and plays irreplaceable role because of its predominant properties. Therefore, the study on supercapacitor has drawn more attention.Electrode materials are the key part of supercapacitor. In this dissertation, activated carbon electrode, polyaniline/activated (PANI/AC) electrode, Poly (2, 5-dihydroxyaniline)/activated (PDHA/AC) electrode were prepared. The morphologies and electrochemical properties of those electrodes were investigated by scanning electronic microscope (SEM), cyclic voltammetry (CV), galvanostatic charge-discharge, electrochemical impedance spectroscopy (EIS), cycle life test. The main contents of this dissertation are as the following:1. Preparation and electrochemistry performance of activated carbon electrodesPreparation process of AC electrode was investigated. AC electrode was prepared successfully. CV curve of AC electrode shows rectangular-like feature; potential-time of galvanostatic charge-discharge curve shows linear relationship; EIS indicates: internal resistance of activated carbon electrode is about 2.5Ω, charge-transfer resistance is about 1Ω. At current density of 3 mA·cm-2, specific capacitance of AC electrode is 285.60 F·g-1, At current density of 10 mA·cm-2, specific capacitance is about 63.9% of the specific capacitance at current density of 3 mA·cm-2. Specific capacitance remains fairly constant up to 150 cycles during charge-discharge cycles.2. Preparation and electrochemistry performance of polyaniline/activated carbon (PNAI/AC) electrodes The aim of this part is to prepare high capacitance PNAI/AC electrode which has good electrochemical performance. PANI was loaded on AC electrode by different methods. PANI/AC electrode was prepared successfully. The electrochemical performance was investigated.(1) PANI/AC electrode was prepared by cyclic voltammetry (-0.2V-0.8V,7 cycles). SEM shows the diameter of nanorod polyaniline is about 100 nm, the overall morphology presents network morphology. PANI/AC electrode shows redox peaks in CV curve and voltage plateaus in galvanostatic charge/discharge curve. From the impedance spectra, the internal resistance of AC and composite is about 2.5Ω, it is clearly seen that charge-transfer resistance of PANI/AC composite electrode is smaller than pure AC electrode at potential of 0.4 V, further proving that PANI coated on AC electrode have excellet conductivity. The PANI/AC composite electrodes showed much higher specific capacitance (758.53 F·g-1) which is as 2.7 times as capacitance of AC electrode, better power characteristics. At current density of 3 mA·cm-2, the maintenance of the capacitance is about 82.01% during 400 cycles. At current density of 5 mA·cm-2, the maintenance of the capacitance is about 83.42% during 600 cycles.(2) PNAI/AC electrode was prepared by cyclic voltammetry (CV) (-0.2V-0.9V,4 cycles). PANI/AC electrode shows redox peaks in CV curve and voltage plateaus in galvanostatic charge-discharge curve. EIS test indicate:the internal resistance of AC and composite is about 2.7Ω, charge-transfer resistance of PANI/AC composite electrode is smaller than pure AC electrode at potential of 0.4V. The specific capacitance of PANI/AC composite electrodes is about 758.53 F·g-1, which is as 2.7 times as capacitance of AC electrode. However, the power characteristics needs improvement. At current density of 3 mA·cm-2, the maintenance of the capacitance is about 67.15% during 411 cycles. At current density of 5 mA·cm-2, the maintenance of the capacitance is about 95.5% during 350 cycles.(3) PNAI/AC electrode was prepared by potentiostatically. SEM indicate the diameter of polyaniline is about 100 nm; PANI/AC electrode shows redox peaks in CV curve, however, the curves of composite become deformed compared with composite prepared by cyclic voltammetry; Electrode shows voltage plateaus in galvanostatic charge/discharge curve. EIS indicate:charge transfer impedance of composite is larger than AC electrode even at potential of 0.4V. At current density of 3 mA·cm-2, specific capacitance of PANI/AC composite electrodes is about 473.52F·g-1, which is higher than capacitance of AC electrode, but it is much lower than composite prepared by cyclic voltammetry. At current density of 3 mA·cm-2, the maintenance of the capacitance is about 71.8% during 370 cycles. At current density of 5 mA·cm-2, the maintenance of the capacitance is about 82.0% during 290 cycles.3. Preparation and electrochemical performance of Poly (2,5-dihydroxyaniline) /activated carbon (PDHA/AC) composite electrode(1) Poly (2,5-dihydroxyaniline) powder was prepared by chemical oxidation, firstly, activated carbon, C, polyvinylidene fluoride (PVDF), Poly (2, 5-dihydroxyaniline) were mixed, Poly (2,5-dihydroxyaniline)/activated carbon (PDHA/AC) composite electrode was prepared through preparation process of AC electrode. PDHA/AC electrode shows redox peaks in CV curve and voltage plateaus in galvanostatic charge-discharge curve. From the impedance spectra, the charge transfer impedance of PDHA/AC composite electrode is smallest at potential of 0.4V. This is consistent with the CV and galvanostatic charge/discharge test.At current density of 5 mA·cm-2, capacitance remains constant up to 290 cycles. At current density of 10 mA·cm-2, capacitance remains 75.75% during 572 cycles.(2) Fistly, poly (2,5-dihydroxyaniline) film on AC electrode was obtained though electrochemical method. From SEM photos, nanofiber PDHA interwined together to form a three-dimensional reticulation; Compared with activated carbon electrode, PDHA/AC electrode has higher current and shows redox peaks in CV curve and voltage plateaus in galvanostatic charge-discharge curve. From the impedance spectra, the internal resistance of AC and composite is about 2.8Ω, it is clearly seen that charge-transfer resistance of PDHA/AC composite electrode is smaller than pure AC electrode at potential of 0.4V, further proving that PDHA coated on AC electrode have excellet active sites and conductivity. At current density of 3 mA·cm-2, PDHA/AC electrode shows higher specific capacitance of 958.51 F·g-1 which is as 3.5 times as capacitance of AC electrode, better power characteristics, and also the capacacitance is higher than that of PANI/AC electrode; The maintenance of the PDHA/AC composite electrodecapacitance is about 90.34% during the charge-discharge cycles.