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Author ORCID Identifier

https://orcid.org/0000-0002-8782-2116

AccessType

Open Access Dissertation

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2024

Month Degree Awarded

February

First Advisor

James J. Watkins

Second Advisor

Reika Katsumata

Third Advisor

Nianqiang Wu

Subject Categories

Other Materials Science and Engineering | Polymer and Organic Materials | Structural Materials

Abstract

Carbonaceous material including porous carbon and graphene are extensively investigated and employed in numerous application areas especially energy storage and conversion, filtration, catalysis, and mechanical metamaterial enabled by their exceptional properties. However, producing these material often demand precise control over structure property relationship and also involve extremely high temperature in inert atmosphere with long processing time which has been a limiting factor in their high throughput production. This dissertation presents technological innovation in producing carbonaceous material (i.e., graphene and porous carbon) using simple yet effective and scalable approach with the focus on improving their energy storage capabilities for both micro and structural devices. Chapter 1 introduces the concept of supercapacitors a promising next generation energy storage devices with the brief discussion on the current fabrication method of porous carbon and graphene as a super capacitive electrode material. Chapter 2 presents a photothermal method for fast, efficient, and scalable preparation of high-quality, few-layer graphene films on large area. The process involves one step photothermal conversion of polymeric material into graphene using high intensity xenon flash lamp at ambient conditions without any catalyst. Of various polymeric material investigated, cyclized polyacrylonitrile resulted in the graphene with less defects in its structure as confirmed by Raman spectra. The mechanism of photo thermal conversion of polymeric material into graphene is also elucidated. Moreover, the utility of the photothermally produced graphene is demonstrated by preparing graphene film electrodes onto a carbon fiber current collector for supercapacitors. The graphene electrodes exhibited capacitance of 3mF/cm2 a nominal regime for carbon-based devices. Chapter 3 builds upon the previous chapter and focuses on the preparation of high-performance supercapacitor using the already developed photothermal processing. Specifically, polyaniline a rod like polymer resulted in the graphene with interconnected porous structure and oxygen doping a desired trait for supercapacitors. Along with it, polyaniline offered several additional advantages as compared to polymers explored in previous chapter for graphene preparation such as it can be grown electrochemically on conducting substrates enabling the rapid synthesis of polymeric material directly onto the desired substrate, including carbo fiber. A remarkable capacitance in excess of 150 mF/cm2 (at least fortyfold increase compared to graphene produced conventionally) is obtained for polyaniline derived graphene without any post processing/modification. Furthermore, the photothermal strategy allowed the one-step preparation of supercapacitor devices on areas exceeding 100 cm2, yielding an absolute areal capacitance of 4.5 F. The proportional increase in capacitance with device area facilitates scaling and suggests the commercial applicability of this sustainable approach for low-cost, energy-efficient, and high-throughput production of lightweight, high-performance graphene-based supercapacitor devices. Chapter 4 introduces the preparation of large-pore (40 nm) ordered mesoporous carbon by rapid thermal annealing (RTA) of precursor films structured by brush block copolymer-mediated self-assembly. Ultrafast RTA processing (~50oC/s) at elevated temperatures (up to 1000oC) allowed the generation of stable, conductive, turbostratic mesoporous carbon films in minutes. Porous carbon prepared on stainless steel at 900oC demonstrated exceptionally high areal and volumetric capacitances of 6.3 mF/cm2 and 126 F/cm3 (at 0.8 mA/cm2 using 6M KOH as the electrolyte), and 91% capacitance retention after 10,000 galvanostatic charge/discharge cycles. Post-RTA conformal V2O5 deposition yielded pseudo capacitors with 10-fold increases in energy density (20 μWh cm-2 μm-1) without adversely affecting the high-power density (450 μW cm-2 μm-1). The use of RTA coupled with BBCP templating opens avenues for scalable, rapid fabrication of high-performing carbon-based micro-pseudocapacitors. Chapter 5 builds upon the previous chapter by integrating the self -assembled of brush block copolymer with nano imprinting lithography to increase the performance of micro-supercapacitor on limited footprint area. In this project, high aspect ratio nanofeature of porous carbon was prepared to increase the accessible surface area per unit area. Mechanical properties of nanoporous carbon were also determined. Remarkably, these material exhibit ultrahigh strength similar to or even higher than the tenth of Young's modulus (E), the most widely used approximation of a fundamental upper limit of material breaking strength. None of the engineering materials exhibit a comparable combination of density, strength, deformability, and damping capability. The results of this study provide a great promise of amorphous carbon nanopillars and their nanoporous structures as a superior structural nanomaterial.

DOI

https://doi.org/10.7275/36499144

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