The New Jersey Institute of Technology's
Electronic Theses & Dissertations Project

Title:	Supercapacitors with gate electrodes
Author:	Chowdhury, Tazima Selim
View Online:	njit-etd2019-027 (xix, 112 pages ~ 6.3 MB pdf)
Department:	Department of Electrical and Computer Engineering
Degree:	Doctor of Philosophy
Program:	Electrical Engineering
Document Type:	Dissertation
Advisory Committee:	Grebel, Haim (Committee chair) Tsybeskov, Leonid (Committee member) Barat, Robert Benedict (Committee member) Ko, Dong Kyun (Committee member) Liu, Xuan (Committee member)
Date:	2019-05
Keywords:	Cyclic voltammetry Electrochemical impedance spectroscopy Electrodes Electrolytes Separator Supercapacitors
Availability:	Unrestricted
Abstract:	A new approach to improve the capacitance of supercapacitors (SC) is proposed in this study. A typical SC is composed of an anode and a cathode; a separator in between them assures an unintentional discharge of the capacitor. The study focuses on a family of structured separators, either electronically active or passive which are called gates. An active structured separator layer has been fabricated and analyzed. The structured separator has characteristics of electrical diode and is fabricated out of functionalized carbon nanotubes (CNT). Improvement of the overall capacitance of SC, equipped with either active or passive structured separators demonstrated a large capacitance increase compared to SC which are interfaced with traditional separators. Cyclic voltammetry (CV), Chrono-potentiometry (charge-discharge, C-D) and Electrochemical Impedance Spectroscopy (EIS) are used to assess the electrochemical characteristics of these novel devices. Raman spectroscopy is used to assess the quality of the structured CNT. Scanning electron microscope determines the surface morphology and porosity of the films. Current-voltage measurement takes place to ensure non-linear characteristics of the fabricated active separator layer. CV demonstrates that aqueous based electrolyte supercapacitors (SC) does not exhibit reaction peaks. Chrono-potentiometry demonstrates an overall 5-10% larger capacitance then traditional counterparts. EIS exhibits an unusual reduction of the cell's equivalent series resistance (ESR). Additional capacitance increase can be achieved when the active structured separator is biased between -0.1 V to +0.1 V. The electrical energy, invested in a biased gate is fully captured as a stored energy. A similar study is performed by fabricating active separator interfacing with ionic liquid electrolyte. Active gates exhibit similar capacitance improvement even after many cycles of charge and discharge when they are interfaced with ionic liquid.