Dissertation > Industrial Technology > Electrotechnical > Electrical > Capacitor

Study of Carbon-based Electrochemical Double Layer Capacitor

Author ChengHongPing
Tutor WeiZiDong
School Chongqing University
Course Physical and chemical
Keywords EDLC thiourea psuedocapacitance
Type Master's thesis
Year 2007
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Electrochemical capacitors have been recognized as unique energy storage devices which can provide energy densities higher than those of conventional electrolytic capacitors, and higher power density and longer cycle life than batteries, filling the gap between conventional dielectric capacitors and batteries. Thus, electrochemical capacitors are widely applied in different fields, for example, power requirement, energy storage and composite systems included electrochemical capacitors and batteries. Just now, the studies on electrochemical capacitor are mainly focused on electrochemical double layer capacitor (EDLC) and the capacitor with psuedocapacitance.In this paper, the simulative capacitor has been fabricated by activated carbon as electrode materials. The performance of the capacitor was studied by cyclic voltammograms, constant current charge/discharge methods and impedance test. The results show that the capacitor has the typical character of capacitance. The efficiency of charge/discharge is higher 90%, the capacitance of activated carbon electrode reaches 137.5F/g when the current density is 10mA (0.25A/g).The potential changes of single electrode was studied when the capacitor was charging or discharging, the data show that the specific capacitance of positive electrode is 101.13F/g and the capacitance of negative electrode is 187.96F/g. Moreover, the resistance of positive electrode is higher negative electrode.On the basis of principium of inhibitors, thiourea was added to the alkaline solution. And then, the effect of thiourea on capacitor was studied. The results show that the capacitance of capacitor increase form 107F/g to 137.5F/g when the current density is 20mA(0.5A/g).For a while, the performance of cycle was improved. The electrode and capacitor were studied by impedance spectroscopy and constant current charge/discharge. The reason for higher capacitance was the process of ionic’s diffusion was restrain by added thiourea, and the sorption of thiourea causes an increase in the performance of cycle.The activated carbon was loaded with some iron hydroxide particles to a composite electrode material, the simulative capacitor was assembled with the composite electrode and other active carbon electrode. The result of constant current test show the capacitance is few change when the composite electrode as positive electrode ,but the capacitance of this hybrid capacitor is more than EDLC when the composite electrode as negative electrode. As to single electrode, the specific capacitance is increase about 18%.The analysis consider that the psuedocapacitance of iron oxide which origin from the Faraday reaction give rise to the increase.

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