Date of Award

2018

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering (PhD)

Administrative Home Department

Department of Materials Science and Engineering

Advisor 1

Yun Hang Hu

Committee Member 1

Stephen A. Hackney

Committee Member 2

Loredana Valenzano

Committee Member 3

Shiyue Fang

Abstract

Electric double-layer capacitors (EDLCs), as an indispensable part of renewable energy systems, store energy by electrostatic charge accumulation on the surface of porous carbon materials. Their performance strongly associates with surface area, and electronic/ionic conductivity. 2D graphene with surface area of 2630 m2/g, high conductivity, and theoretical gravimetric capacitance of 526 F/g, attracts great attention in EDLCs. Meanwhile, practical application requires graphene electrodes with a mass loading up to 10 mg/cm2 or thickness of 200 µm and prefers well-balanced gravimetric/areal/volumetric capacitances. However, 2D graphene at bulk states would lose its features from atomically single or few-layer graphite sheets, leading to poor electrochemical performance. Thus, 3D graphene is thought to be the most effective strategy to face the challenges. Herein, we utilized a series of invented reactions to synthesize 3D cauliflower-fungus-like graphene (chapter 3), 3D surface-microporous graphene (chapter 4), meso/macro-porous frameworks of surface-microporous graphene (chapter 5), 3D potassium-ion preintercalated graphene (chapter 6), and sodium-embedded carbon nanowalls (chapter 7), and dense meso-porous carbon (DMPC, chapter 8). We employed these novel graphene as large mass-loading electrodes for symmetrical EDLCs and investigated their gravimetric/areal/volumetric performance at high rate within wide-operating temperature range. In this dissertation, a critical issue that the enhancement of mass loading usually sacrifices the gravimetric capacitance has been solved. Thus, we achieved ultrahigh areal capacitance for graphene-based EDLCs. Besides, a highly dense but mesoporous carbon material was successfully synthesized by reaction between Li liquid and CO gas. It solved the trade-off issue among gravimetric, areal, and volumetric capacitances. With an ultrahigh packing density of 1.94 g/cm3, DMPC can achieve an ultrahigh areal capacitance of 2.15 F/cm2 with mass loading of 11.5 mg/cm2, as well as large gravimetric capacitance of 205.2 F/g and volumetric capacitance of 220.5 F/cm3. These graphene materials provide great potential for commercial application.

Capacitive deionization (CDI) is one of the most promising technologies for water treatment. The efficient ion removal from brackish water or seawater is based on the formation of electric double layers on the surface of electrode materials at low power supply. Thus, electrode materials can significantly affect its performance. Herein, we utilized Na-embedded carbon nanowalls (Na@C, chapter 9.1), and honeycomb graphene clusters (HGC, chapter 9.2) as electrodes for CDI cells. In a batch-mode configuration, Na@C can receive a electrosorption capacity of 8.75 mg/g in 100 mg/l NaCl, and HGC can achieve electrosorption capacity of 14.08 mg/g in 5 mM NaCl.

Available for download on Tuesday, April 30, 2019

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