Design, Fabrication, and Characterization of Nanostructured Pseudocapacitive Coatings on Vertically Aligned Carbon Nanotube Electrodes for High Performance 3D Microsupercapacitors
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Zhang, Yumeng
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Abstract
Microsupercapacitors (MSCs) are microfabricated energy storage devices that utilize the rapid adsorption and desorption of ions at the electrode/electrolyte interface to store charge or electrical energy. To enable a microscale size, potential for on-chip integration with other electronics, and more rapid charge/discharge rates, MSCs are microfabricated with planar interdigital electrodes which differs from the conventional stacked electrode architecture of typical supercapacitors. Compared to thin film batteries, MSCs have advantages such as higher power density and extended cycle life, but the energy density is lacking. As a result, these miniaturized devices are attractive for use as energy storage components for self-powering electronics.
The goal of this study is to improve the energy density and capacitance of 3D MSCs, through novel fabrication processes and material design. This research explores several novel deposition methods and materials for fabricating nanostructured pseudocapacitive coatings on vertically aligned carbon nanotube (VACNT) based electrodes for use in high performance 3D MSCs. The porous structure of VACNT provides high surface area for ion exchange, leading to high capacitance. Additionally, these surfaces could be functionalized by transition conducting polymers, metal oxides, or metal nitrides to increase capacitance via pseudocapacitance. Pseudocapacitive materials store charges via Faradaic reversible redox reactions at the electrode surface. It was demonstrated that incorporating thin and conformal coatings of pseudocapacitive materials onto VACNT electrodes increases the specific capacitance and energy density per area of the 3D MSC device by orders of magnitude while maintaining the conventional advantage of high power density.
Various methods were used to apply pseudocapacitive coating material to VACNT based 3D MSC device to achieve high energy and power densities. This work investigated a variety of approaches such as atomic layer deposition (ALD), electrodeposition (ED), and aerosol jet printing (AJP) to deposit pseudocapacitive materials on VACNT electrodes to create symmetric or asymmetric MSCs. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry (CP) were used to evaluate performance of the developed electrodes and devices. Material characterization techniques including scanning electron microscopy (SEM), energy dispersive x-ray (EDX), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were used to highlight the material structures attributing to the high performance.
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Date
2021-07-14
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Text
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Dissertation