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Fundamentals of the Oxidative Chemical Vapor Deposition of Polyaniline and Its Applications in Supercapacitors.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Fundamentals of the Oxidative Chemical Vapor Deposition of Polyaniline and Its Applications in Supercapacitors./
作者:	Li, Xiaobo.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
面頁冊數:	112 p.
附註:	Source: Dissertations Abstracts International, Volume: 82-04, Section: B.
Contained By:	Dissertations Abstracts International82-04B.
標題:	Chemical engineering. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28086994
ISBN:	9798672150666

Fundamentals of the Oxidative Chemical Vapor Deposition of Polyaniline and Its Applications in Supercapacitors.
Li, Xiaobo.

Fundamentals of the Oxidative Chemical Vapor Deposition of Polyaniline and Its Applications in Supercapacitors. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 112 p.

Source: Dissertations Abstracts International, Volume: 82-04, Section: B.

Thesis (Ph.D.)--Drexel University, 2020.

This item must not be sold to any third party vendors.

Compared to batteries, supercapacitors have higher power density but suffer from lower energy density. To improve energy density, conducting polymers can be used to store charge via energy-dense redox reactions. Together with their ease in synthesis and low cost, conducing polymers are promising electrode materials for supercapacitors. Among different conducting polymers, polyaniline (PANI) is attractive as it has one of the highest specific capacitance. Proposed by Simon and Gogotsi, integrating conducting polymers including PANI with carbon supercapacitors can lead to a synergetic effect that takes advantage of both the carbon and conducting polymer materials. Traditional integration methods are based on liquid processing. Due to the low solubility of PANI and the wetting issues of liquids, these methods have limited abilities in effectively integrating PANI into nanoscale carbon materials. Here, a liquid-free oxidative chemical vapor deposition (oCVD) approach aims to overcome these challenges. Instead of relying on PANI solutions, oCVD utilizes vaporized aniline monomers and transition metal halide oxidants as precursors to synthesize solid PANI polymer thin films on surfaces under low pressure. By utilizing gas phase reactants, both reactants can easily diffuse through nanoscale carbon substrates, adsorb onto the surface and then initialize the polymerization, which will result in conformal and uniform coatings. Additionally, processing parameters of oCVD, including substrate temperature, operating pressure and reactant flow rates, can be easily and precisely tuned. Previous studies have shown that by optimizing the deposition conditions, emeraldine PANI, which is the electrically conductive state of PANI, can be conformally and uniformly deposited onto carbide derived carbon (CDC) supercapacitor electrodes. This composite showed enhanced charge storage ability.To further enhance the performance and robustness of carbon supercapacitors, free-standing carbon electrodes are promising as they do not require binders or additional current collector components, which add dead weight. Therefore, here, free-standing electrospun carbon nanofibers (CNFs) have been used as the carbon supercapacitor base on which oCVD PANI is integrated. By optimizing oCVD processing conditions, conformal and uniform PANI coatings onto CNFs are achieved, which result in 98% capacitance retention from 10 to 600 mV/s, a high columbic efficiency of ~100% over 3000 cycles, and capacitance of ~149 F/g at 1 A/g. A post-deposition washing is found to enhance electrochemical performance as it creates a rough PANI surface.One of the challenges with integrating PANI onto free-standing CNFs is understanding how to achieve uniform PANI coatings from the top to the bottom of the porous CNF mat. Previous polymer CVD work has shown that controlling adsorption and reaction is key to enabling uniform and conformal depositions in porous substrates. Therefore, here, oCVD processing has been studied by understanding the effect of substrate temperature on polymer growth. Substrate temperature has a direct impact on both adsorption and reaction. By varying the substrate temperature from 70 to 150 °C, oCVD PANI growth is found to have two different deposition regimes. At temperatures below ~90 °C, polymer growth is reaction-limited while, at higher temperatures, growth becomes adsorption-limited as indicated by a negative Arrhenius activation energy. In this latter regime, more uniform and conformal PANI coatings can be achieved, and in this higher temperature region, more polymeric (vs. oligomeric) PANI is formed.Besides substrate temperature, the oxidant plays an important role in achieving oxidative polymerization of PANI. Previous oCVD studies have focused primarily on FeCl3 and SbCl5 oxidants, both of which are heavy precursors and have low vapor pressures that favor strong adsorption. To reduce adsorption, here, VOCl3 is investigated as an oxidant that has higher vapor pressure and therefore favor an adsorption-limited growth found to produce more uniform and conformal coatings. Preliminary results with using VOCl3 (vs. SbCl5) have not only shown this is true, but higher quality emeraldine PANI can be synthesized with significant crystalline formation, which has not been reported before for oCVD PANI. Previous studies show that crystalline structures in PANI enhance electrical conductivity, which could help enhance PANI performance in supercapacitor electrodes by reducing series resistance. Additionally, from preliminary experiments, the oxidant-to-monomer ratio impacts crystal size. Therefore, the final steps in this research are to understand the influence of oCVD processing on PANI crystallization in order to enhance PANI performance in supercapacitors.

ISBN: 9798672150666Subjects--Topical Terms:

560457
Chemical engineering.
Subjects--Index Terms:

Conducting polymers

Fundamentals of the Oxidative Chemical Vapor Deposition of Polyaniline and Its Applications in Supercapacitors.
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500 $a Source: Dissertations Abstracts International, Volume: 82-04, Section: B.
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502 $a Thesis (Ph.D.)--Drexel University, 2020.
506 $a This item must not be sold to any third party vendors.
520 $a Compared to batteries, supercapacitors have higher power density but suffer from lower energy density. To improve energy density, conducting polymers can be used to store charge via energy-dense redox reactions. Together with their ease in synthesis and low cost, conducing polymers are promising electrode materials for supercapacitors. Among different conducting polymers, polyaniline (PANI) is attractive as it has one of the highest specific capacitance. Proposed by Simon and Gogotsi, integrating conducting polymers including PANI with carbon supercapacitors can lead to a synergetic effect that takes advantage of both the carbon and conducting polymer materials. Traditional integration methods are based on liquid processing. Due to the low solubility of PANI and the wetting issues of liquids, these methods have limited abilities in effectively integrating PANI into nanoscale carbon materials. Here, a liquid-free oxidative chemical vapor deposition (oCVD) approach aims to overcome these challenges. Instead of relying on PANI solutions, oCVD utilizes vaporized aniline monomers and transition metal halide oxidants as precursors to synthesize solid PANI polymer thin films on surfaces under low pressure. By utilizing gas phase reactants, both reactants can easily diffuse through nanoscale carbon substrates, adsorb onto the surface and then initialize the polymerization, which will result in conformal and uniform coatings. Additionally, processing parameters of oCVD, including substrate temperature, operating pressure and reactant flow rates, can be easily and precisely tuned. Previous studies have shown that by optimizing the deposition conditions, emeraldine PANI, which is the electrically conductive state of PANI, can be conformally and uniformly deposited onto carbide derived carbon (CDC) supercapacitor electrodes. This composite showed enhanced charge storage ability.To further enhance the performance and robustness of carbon supercapacitors, free-standing carbon electrodes are promising as they do not require binders or additional current collector components, which add dead weight. Therefore, here, free-standing electrospun carbon nanofibers (CNFs) have been used as the carbon supercapacitor base on which oCVD PANI is integrated. By optimizing oCVD processing conditions, conformal and uniform PANI coatings onto CNFs are achieved, which result in 98% capacitance retention from 10 to 600 mV/s, a high columbic efficiency of ~100% over 3000 cycles, and capacitance of ~149 F/g at 1 A/g. A post-deposition washing is found to enhance electrochemical performance as it creates a rough PANI surface.One of the challenges with integrating PANI onto free-standing CNFs is understanding how to achieve uniform PANI coatings from the top to the bottom of the porous CNF mat. Previous polymer CVD work has shown that controlling adsorption and reaction is key to enabling uniform and conformal depositions in porous substrates. Therefore, here, oCVD processing has been studied by understanding the effect of substrate temperature on polymer growth. Substrate temperature has a direct impact on both adsorption and reaction. By varying the substrate temperature from 70 to 150 °C, oCVD PANI growth is found to have two different deposition regimes. At temperatures below ~90 °C, polymer growth is reaction-limited while, at higher temperatures, growth becomes adsorption-limited as indicated by a negative Arrhenius activation energy. In this latter regime, more uniform and conformal PANI coatings can be achieved, and in this higher temperature region, more polymeric (vs. oligomeric) PANI is formed.Besides substrate temperature, the oxidant plays an important role in achieving oxidative polymerization of PANI. Previous oCVD studies have focused primarily on FeCl3 and SbCl5 oxidants, both of which are heavy precursors and have low vapor pressures that favor strong adsorption. To reduce adsorption, here, VOCl3 is investigated as an oxidant that has higher vapor pressure and therefore favor an adsorption-limited growth found to produce more uniform and conformal coatings. Preliminary results with using VOCl3 (vs. SbCl5) have not only shown this is true, but higher quality emeraldine PANI can be synthesized with significant crystalline formation, which has not been reported before for oCVD PANI. Previous studies show that crystalline structures in PANI enhance electrical conductivity, which could help enhance PANI performance in supercapacitor electrodes by reducing series resistance. Additionally, from preliminary experiments, the oxidant-to-monomer ratio impacts crystal size. Therefore, the final steps in this research are to understand the influence of oCVD processing on PANI crystallization in order to enhance PANI performance in supercapacitors.
590 $a School code: 0065.
650 4 $a Chemical engineering. $3 560457
650 4 $a Physical chemistry. $3 1981412
653 $a Conducting polymers
653 $a Kinetics
653 $a Oxidative chemical vapor deposition
653 $a Polyaniline
653 $a Supercapacitor
690 $a 0542
690 $a 0494
710 2 $a Drexel University. $b Chemical Engineering (College of Engineering). $3 3195086
773 0 $t Dissertations Abstracts International $g 82-04B.
790 $a 0065
791 $a Ph.D.
792 $a 2020
793 $a English
856 4 0 $u https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28086994