<p> Cathodic electrodeposition method has been developed for the fabrication of manganese oxide films for application in electrochemical supercapacitors (ES). The manganese oxide films prepared from KMn04 and NaMn04 aqueous solution showed an increasing deposition yield with the deposition time. The deposition rate decreases with increasing the concentration of deposition precursor. The obtained films were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), thermogravimetric and differential thermal analysis (TGA/DTA). The SEM observations revealed uniform films of highly porous nanostructure on different substrates. The capacitive behavior of the deposits was investigated by cyclic voltammetry and chronopotentiometry method in 0.1M NaS04 aqueous solutions. As prepared deposits exhibited pseudocapacitive behavior in the potential window of 0-1.0 V versus SCE with excellent cyclability. A maximum specific capacitance (SC) of 353 Fig was obtained for the 45 μg/cm2 film deposited from KMn04 solution on stainless steel foil, at a scan rate of 2 m V /s in the 0.1 M Na2S04 solution. It was found that the SC decreased with increasing deposit thickness and scan rate. No significant effect was obtained on the films prepared from 20 mM KMn04 on stainless steel after heat treatment at various temperatures. The capacitance of as-prepared electrode did not change by changing the electrolyte from Na2S04 to K2S04 solutions. However, higher capacitance values were observed by using electrolyte with higher concentration. Different structures of manganese oxides were obtained when different deposition precursors were used. No significant difference in capacitive behavior was found between the films prepared from different deposition precursor. However it was concluded that conductivity of the film is key in determining the performance of the electrodes. The effect of substrates on the electrochemical behavior has also been investigated by using stainless steel and nickel foils. </p> / Thesis / Master of Applied Science (MASc)

Neste trabalho foi proposto investigar as características de capacitores eletroquímicos de dupla camada elétrica (supercapacitores) utilizando como matéria prima um eletrólito biocompatível como rota viável de baixo custo econômico para obtenção de dispositivos eletrônicos para armazenamento de energia. O objetivo principal foi estudar a influência dos vários parâmetros de processamento nas características elétricas de supercapacitores à base de eletrólito neutro, utilizando, na preparação dos eletrodos oxido de grafeno reduzido via HDDR 400°C e o carbono ativado, também com baixa toxidade e impacto ambiental. O primeiro tópico consistiu na preparação de eletrólitos com diferentes concentrações para avaliar este parâmetro na curva de autodescarga dos supercapacitores. Alternativamente realizou-se a caracterização dos eletrodos preparados com oxido de grafeno reduzido via HDDR 400°C e carbono ativado por ensaios de voltametria cíclica em um analisador eletrônico computadorizado de supercapacitores, que resultou na determinação da capacitância específica do material precursor e das resistências internas. Foram utilizadas técnicas adicionais para caracterização dos materiais precursores e processados, tais como: microscopia eletrônica de varredura (MEV-EDS), difração de raios-X (DRX). / On this work was proposed research the electrochemical double layer capacitors characteristics (supercapacitors) using an environmentally compatible electrolyte as viable low economic cost path to obtain electronics devices for energy storage. The mains objective was to study the influence of the various processing parameters on electrical characteristics of supercapacitors based in neutral electrolyte, using in the preparation the activated carbon and reduced graphene oxide HDDR 400°C, also with low toxicity and environmentally impact. The first topic consisted in the preparation of electrolytes with different concentrations to evaluate this parameter in the self-discharge curve of supercapacitors. Alternatively was made characterization experiments of the activated carbon electrodes and rGO HDDR 400°C by cyclic voltammetry essays in an electronic computerized analyzer of supercapacitors that resulted in the determination of the precursor material specific capacitance and internal resistances Was utilized additional technics for characterization of precursor materials such as scanning electron microscopy (MEV-EDX) and X-ray diffraction (DRX).

<p> Electrochemical supercapacitors (ES) are urgently needed as components in many advanced power systems. The development of advanced ES is expected to enable radical innovation in the area of hybrid vehicles and electronic devices. Nanostructured manganese oxides in amorphous or various crystalline forms have been found to be promising electrode materials for ES. The use of composite electrodes of manganese oxide with carbon nanotubes is being proposed to improve the overall electrochemical performance of the ES.</p> <p> Electrodeposition methods have been developed for the fabrication of manganese oxide films with/without carbon nanotubes for applications in ES. Electrolytic deposition of manganese oxides was found to be possible using Mn2+ and Mn7+ species, co-deposition of multi wall carbon nanotubes (MWNT) and manganese oxide using cathodic electrosynthesis was successfully achieved.</p> <p> Novel chemical process has been developed for the synthesis of nano-size manganese oxide particles. Electrophoretic deposition of the nano-size manganese oxide particles was able to be performed in both aqueous and non-aqueous solutions. Electrophoretic co-deposition of the nano-size manganese oxide particles with carbon nanotubes was successfully achieved.</p> <p> The mechanisms and kinetics of all the deposition methods are discussed. Charge storage properties of the films prepared by different deposition methods are investigated and compared.</p> / Thesis / Master of Applied Science (MASc)

This research is aimed at synthesizing millimeter-scale carbon nanotube arrays (CNTA) by conventional chemical vapor deposition (CCVD) and water-assisted chemical vapor deposition (WACVD) methods, and exploring their application as catalyst supports for electrochemical supercapacitors. The growth mechanism and growth kinetics of CNTA under different conditions were systematically investigated to understand the relationship among physical characteristics of catalyst particles, growth parameters, and carbon nanotube (CNT) structures within CNTAs. Multiwalled CNT (MWCNT) array growth demonstrates lengthening and thickening stages in CCVD and WACVD. In CCVD, the lengthening and thickening were found to be competitive. By investigating catalyst particles after different pretreatment conditions, it has been found that inter-particle spacing plays a significant role in influencing CNTA height, CNT diameter and wall number. In WACVD, a long linear lengthening stage has been found. CNT wall number remains constant and catalysts preserve the activity in this stage, while MWCNTs thicken substantially and catalysts deactivate following the previously proposed radioactive decay model in the thickening stage of WACVD. Water was also shown to preserve the catalyst activity by significantly inhibiting catalyst-induced and gas phase-induced thickening processes in WACVD. Mn3O4 nanoparticles were successfully deposited and uniformly distributed within millimeter-long CNTAs by dip-casting method from non-aqueous solutions. After modification with Mn3O4 nanoparticles, CNTAs have been changed from hydrophobic to hydrophilic without their alignment and integrity being destroyed. The hydrophilic Mn3O4/CNTA composite electrodes present ideal capacitive behavior with high reversibility. This opens up a new route of utilizing ultra-long CNTAs, based on which a scalable and cost-effective method was developed to fabricate composite electrodes using millimeter-long CNTAs. To improve the performance of the composites, -MnO2 nanorods were anodically pulse-electrodeposited within hydrophilic 0.5 mm-thick Mn3O4 decorated CNTAs. The maximum gravimetric capacitance for the MnO2 nanorods/CNTA composite electrode was found to be 185 F/g, and that for -MnO2 nanorods was determined to be 221 F/g. After electrodeposition, the area-normalized capacitance and volumetric capacitance values were increased by a factor of 3, and an extremely high area-normalized capacitance of 1.80 F/cm2 was also achieved for the MnO2 nanorods/CNTA composite. / Materials Engineering

No description available.

Electrochemical supercapacitors (ESs) are one of the most modern energy storage systems that offer a balance between power and energy densities in which the energy storage mechanisms could be an electrostatic double layer (EDLCs) and pseudocapacitive. In this thesis, hybrid asymmetric supercapacitors have been developed to optimize the advantages for different types of (ESs) such as high conductivity, stability, fast charge-discharge, and relatively high performance. These developments include high active mass loading electrodes based on multiwall carbon nanotubes (MWCNTs) and transition metal oxides with incubation of low binder percentage and a high mass loading of 40 mg cm-2 that guarantees high electrochemical performance at a wide potential range for different electrodes, especially the cathodic one. Novel synthesis techniques and different multi-dispersants have been demonstrated; a conception colloidal fabrication method has been developed to improve the morphology/dispersion for composites of Fe3O4/MWCNTs (M-CNTs) and NiFe2O4/MWCNTs. Firstly, an advanced synthesis method called particle extraction through a liquid-liquid interface (PELLI) has been developed to enhance the dispersion of the nanoparticles M-CNTs. Furthermore, palmitic acid (PA) has been used as a surfactant in the bottom-up (PELLI) to reduce the agglomeration of M-CNTs with high Gamma (𝛾𝛾) ratio (nanoparticles/MWCNTs). Moreover, different synthesis methods have been developed in the presence of celestine blue dye (CB) as a co-dispersant with advanced electrostatic interaction and coagulation mechanism that ensured well- dispersed of (Fe3O4, NiFe2O4) coated (MWCNTs) at high mass loading. Subsequently, more optimizations have been done to analyze the effect of different adsorption mechanisms by using other co-dispersant agents such as pyrocatechol violet (PV), azure A chloride (AA), and m-cresol purple (CP). Finally, cyclic voltammetry, galvanic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and cyclic stability have been done for the fabricated electrodes and devices in neutral aqueous electrolytes that showed a relevant electrochemical performance in a large potential range. / Thesis / Doctor of Philosophy (PhD) / The rapid increase in human population has caused many economic problems, one of them the enormous energy consumption rate as compared to the limitations of sources available for clean and renewable energy sources. Energy storage systems can be classified into different types, e.g., chemical, electrochemical, thermal, and mechanical systems. Popular electrochemical energy storage systems, such as batteries and capacitors, are used for many important daily applications but have difficulties while optimizing power and energy densities. Here, electrochemical supercapacitors (ESs) are considered potential energy storage systems that could balance power and energy densities with fast charge-discharge and a long lifetime. The purpose of this research is to advance nanocomposite materials for electrochemical supercapacitor applications, where we use new colloidal approaches to fabricate high-performance electrochemical supercapacitor electrodes and devices. Our results reveal that these devices can have exceptional performance that facilitates new routes for their development.

<p>Electrochemical supercapacitors (ES) have become an attractive research interest in advanced power systems and found many applications as an energy storage device in number of areas. The fabrication of advanced electrodes with novel materials and new techniques plays a key part in determining the properties of ES. Conducting polymer polypyrrole (PPY) has been found to be a promising electrode material for ES due to its high pseudo-capacitance and good electrical conductivity.</p> <p>Polypyrrole (PPY) films were successfully obtained on stainless steel substrates by anodic electropolymerization. Anionic dopants such as 2,6-naphthalenedisulfonic acid disodium salt (NSA), chromotropic acid disodium salt (CHR) and gallic acid were used for the synthesis of PPY. The roles of additives in the electrodeposition process have been discussed. The deposition was performed galvanostatically or potentiodynamically and the electrochemical properties of PPY have been investigated and compared by using different characterization techniques.</p> <p>The comparison of the experimental data for NSA, CHR and gallic acid showed the influence of aromatic ring and OH groups on the capacitive behaviour of PPY films. Adherent PPY films were obtained from pyrrole solutions containing CHR as dopant. The specific capacitance (SC) increased with increasing pyrrole and dopant concentration in the solutions used for deposition. The PPY films prepared on stainless steel substrates by electropolymerization are promising electrode materials for ES.</p> / Master of Applied Science (MASc)

With the discovery of conductivity in doped polyacetylene (PA), a new era in synthetic metals has emerged by breaking the traditionally accepted view that polymers were always insulating. Conducting polymers are essentially characterized by the presence of conjugated bonding on the polymeric back bone, which facilitates the formation of polarons and bipolarons as charge carriers. Among the numerous conducting polymers synthesized to date, polypyrrole (PPy) is by far the most extensively studied because of prodigious number of applications owing to its facile polymerizability, environmental stability, high electrical conductivity, biocompatibility, and redox state dependent physico-chemical properties. Electrochemically prepared PPy is more interesting than the chemically prepared polymer because it adheres to the electrode surface and can be directly used for applications such as supercapacitors, electrochemical sensors, electromechanical actuators and drug delivery systems. In quest for improvement in quality of the device performances in the mentioned applications, micro and nano structured polymeric materials which bring in large surface area are studied. Finding a simple and efficient method of synthesis is very important for producing devices of PPy microstructures. Till date, Hard and soft template methods are the most employed methods for synthesis of these structures. Soft template based electrochemical methods are better than hard template methods to grow clean PPy microstructures on electrode substrates as procedures for removal of hard templates after the growth of microstructures are very complex. As per the literature, there is no unique method available to grow PPy microstructures which can demonstrate several applications. Although gas bubble based soft template methods are exploited to grow conducting polymer microstructures of sizes in few hundreds of micrometers, studies on applications of the same are limited. Hence it is planned to develop procedures to grow microstructures that can be used in several applications. In the current work, PPy microstructures with high coverage densities are synthesized on various electrode substrates by soft template based electrochemical techniques. Hollow, hemispherical and spherical PPy microstructures are developed by a two step method using electro generated hydrogen bubble templates on SS 304 electrodes. In the first step, Hydrogen bubbles are electro generated and stabilized on the electrode in the presence of β- naphthalene sulfonic acid (β-NSA). In the second step, Pyrrole is oxidised over the bubble template to form PPy microstructures. Microstructures (open and closed cups) of average size 15 μm are uniformly spread on the surface with a coverage density of 2.5×105 units /cm2. Globular PPy microstructures are developed by a single step method using concomitantly electro generated oxygen bubble templates on SS 304 electrodes during electropolymerization. Microstructures of average size 4 μm are uniformly spread on the surface with a coverage density of 7×105 units/cm2. Surfactant properties of Zwitterionic 4-(2-hydroxyethyl)-1-piperazine ethane sulfonic acid (HEPES) are exploited for the first time to grow conducting polymer microstructures. Ramekin shaped PPy microstructures are developed using HEPES as the surfactant to stabilize hydrogen bubble templates in a two step electrochemical synthesis method. Microramekins of size 100 µm are uniformly spread on the surface with a coverage density of 3000 units/cm2. Micropipettes and microhorns of PPy are synthesised by a single step electrochemical route using HEPES as a surfactant. Hollow micropipettes of length 7 µm with an opening of 200 nm at the top of the structure are observed. Similarly microhorn/celia structures are observed with length 10-15 µm. Microcelia are uniformly distributed over the surface with each structure having a diameter of 2 µm at the base to 150 nm at the tip. Growth mechanism based on contact angle of the reactant solution droplets on the substrate is proposed. PPy microstructures are characterized by scanning electron microscopy, X-Ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman Spectroscopy and UV-Visible spectroscopy to study morphology, ‘chemical bonding and structure’ , ‘defects and charge carriers’. Applicability of the electrodes with PPy microstructures in supercapacitors is investigated by cyclic voltammetry, chronopotentiometry and electrical impedance spectroscopy. Electrodes developed by all the above methods demonstrated very good supercapacitance properties. Supercapacitor studies revealed very high specific capacitances (580, 915, 728 and 922 F/g,) and specific powers (20, 25, 13.89 and 15.91 kW/kg) for electrodes with PPy microstructures (H2 bubble based two step method, O2 bubble based single step method, HEPES stabilized H2 bubbble method and HEPES based microhorn/celia structures respectively). Supercapacitive behavior of all the electrodes is retained even after an extended charge-discharge cycling in excess of 1500 cycles. Horseradish peroxidase entrapped, bowl shaped PPy microstructures are developed for H2O2 biosensing. Amperometric biosensor has a performance comparable to the sensors reported in the literature with high sensitivity value of 12.8 μA/(cm2.mM) in the range 1.0 mM to 10 mM. Glucose oxidase entrapped PPy amperometric biosensor is developed for Glucose sensing. Sensitivity of 1.29 mA/(cm2.mM) is observed for β-D-Glucose sensing in the 0.1 mM to 5.0 mM range while 58 μA/(cm2.mM) is observed in the 5.0 to 40 mM range. Potentiometric urea sensor with urease entrapped PPy microstructures on SS electrode is developed. It is able to sense urea in the micromolar ranges down to 0.1 μM. It represented an excellent performance with sensitivity of 27 mV/decade. Sensitivity in the micromolar range is 4.9 mV/(μM.cm2). Drug encapsulation and delivery is successfully demonstrated by two actuation means (i) by electrochemical actuation, (ii) by actuation based on pH changes. Concepts are proved by delivering a fluorescent dye into neutral and acidic solutions. Drug delivery is confirmed by UV-Visible spectroscopy and Fluorescence microscopy. Finally, Micro/nanostructures with Tangerine, Hollow globular (Pani Poori), Chip, Flake, Rose, Worm, Horn and Celia shapes are synthesized electrochemically and scanning electron microscopic studies are presented. Controlled growth of microstructures on lithographically patterned gold interdigital electrodes is demonstrated with a future goal of creating addressable microstructures. The studies reported in the thesis provide an insight on various applications of PPy microstructures (supercapacitors, sensors and drug delivery systems) developed by a unique methodology based on electrochemically generated gas bubble templates.