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Preparation of an Electrochemically Modified Graphite Electrode and Its Electrochemical Performance for Pseudo-capacitors

Author: FanXinZhuang
Tutor: WangJia；XuHaiBo
School: Ocean University of China
Course: Marine Chemical Engineering and Technology
Keywords: Electrochemical capacitors Modified graphite electrodes Oxygen-containing functional group Pseudo-capacitance Electro-catalytic
CLC: TM53
Type: PhD thesis
Year: 2011
Downloads: 237
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Abstract

The electrochemical capacitor is a range between the new energy storage device in the conventional capacitor and battery, it has a higher specific energy than a conventional capacitor, the ratio is higher than the battery power. The electrode material is a key factor to determine the performance of electrochemical capacitors, relevant research work has been a hot research field. The paper systematically studied the modified graphite electrode preparation, characterization and Pseudo-capacitance, and conducted in-depth analysis of the mechanism of its quasi-capacitance generated; further modified graphite electrode (MGE) in different electrolytes capacitors and catalytic properties; preparation and preliminary analysis of the performance of polyaniline / modified graphite composite electrode capacitance. Integrated use of scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, low-temperature nitrogen adsorption, Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis, Boehm titration, X-ray photoelectron spectroscopy (XPS) The technical means used to characterize the structure and surface properties of the modified graphite electrode by constant current charge and discharge, cyclic voltammetry, AC impedance method modified graphite electrode and polyaniline / modified graphite composite electrode capacitance performance and in-depth analysis of the modified graphite electrode surface oxygen functional groups on its capacitance performance. The main findings are as follows: studies have shown that constant current step techniques for electrochemical modification of graphite electrodes with excellent quasi-capacitance characteristics, the optimum process parameters: anode current of 200 mA, the cathode current -120 mA, corresponding activation time were 300 s and 100 s, 6 cycles. After the electrochemical modification, smoothing the surface of the graphite electrode becomes rough and porous three-dimensional active layer, having a turbostratic graphite and multi-the microchips layer structure generates a large number of oxygen-containing functional groups on its surface. Modified graphite electrode having a good quasi capacitor characteristics, the specific capacitance of 179.7 F g-1, and having a long cycle life. Quantitative analysis of the number of activated oxygen-containing functional groups of the surface of the graphite electrode, the oxygen-containing groups aligned capacitance characteristics. The results showed that the activation of the surface of the graphite electrode of the hydroxy, carbonyl group, and a carboxyl group can occur between consecutive reversible redox reaction generated by the quasi-capacitor contribution of up to 50% of the total capacitance. By cyclic voltammetry, electrochemical impedance spectroscopy and self-discharge test, study the capacitive behavior of the modified graphite electrode in the electrolyte of different pH values, in-depth analysis and alignment the capacitor mechanism and its contribution. The results show that when the pH value is lower, the redox reaction between a hydroxyl group, a carbonyl group, and a carboxyl group, quasi capacitance to total capacitance of 61%; when the pH is increased from 1 to 2, most of the carboxyl group of the surface of the electrode dissociation, a carboxyl group, a carbonyl group between the oxidation reduction reaction Weighting decreases quasi capacitance also decreases; With further increase of the pH value, the carboxyl group of the surface of the electrode almost completely dissociated, the oxidation-reduction reaction is carried out only between the hydroxyl group and a carbonyl group, quasi-capacitance proportion was only 33% accounted for the major part of the electric double layer capacitor. Quasi-capacitance characteristics of the modified graphite electrode in acidic and neutral solution and evaluated by cyclic voltammetry studies on Cl ^{- , NO ₃ ^{- and the Fe ^{3 / the Fe ^{2 electric catalysis. The results show that under acidic conditions, the modified graphite electrode in H2SO4 solution Hen good quasi-capacitance characteristics, apparent specific capacitance of up to 1.730 F cm ^{^{-2 ; HCl solution also has a good quasi-capacitance characteristics, but modified graphite electrode has a certain electro-catalytic activity (starting potential of chlorine evolution negative shift 238 mV), narrowing its potential window of chlorine evolution reaction; in HNO ₃ Pseudo-capacitance of the solution, but modified graphite electrode reduction reaction of the NO3-ion strong electrical catalysis; modified graphite electrodes for the the Fe ^{3 / Fe < sup> 2 redox redox having strong Electrocatalysis and reversible, and thus Available the the solution Fe ^{3 / Fe ^{2 reaction of storing and releasing energy. When the dielectric from acidic to neutral, although the peak current density has been reduced, but the potential window widened significantly, means of MGE neutral system energy density compared to the acidic system has greatly improved. Preparation of polyaniline / graphite composite electrode modified by electrochemical deposition method and by electrochemical test preliminary evaluation of its quasi-capacitance characteristics found polyaniline modified graphite has a synergistic effect, apparent specific capacitance of up to 2.34 F cm ^{-2 , shows great potential.}}}}}}}}}}

Preparation of an Electrochemically Modified Graphite Electrode and Its Electrochemical Performance for Pseudo-capacitors

Abstract

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