No description available.

A new form of organic energy storage devices (organic capacitors) is presented in the first part of this dissertation. The storage devices are made out of an organic semiconductor material and charge storage elements from synthesized nanoparticles. The semiconducting polymer is obtained by blending poly (vinyl alcohol) and poly (acrylic acid) in crystal state polymers with a known plasticizer; glycerol or sorbitol. Synthesized nanoparticles namely, zinc-oxide (ZnO), erbium (Er), cadmium sulfide (CdS), palladium (Pd) and silver-platinum (AgPt) were used as charge storage elements in fabrication of metal-insulator-semiconductor (MIS) structure. The organic semiconductor and synthesized nanoparticles are tested to evaluate and characterize their electrical performance and properties. Fabrication of the organic capacitors consisted of layer-by-layer deposition and thermal evaporation of the electrode terminals. Capacitance versus voltage (C-V) measurement tests were carried out to observe hysteresis loops with a window gate that would indicate the charging, discharging and storage characteristics. Experimental investigation of various integrated energy harvesting techniques combined with these organic based novel energy storage devices are performed in the second part of this dissertation. The source of the energy is the wind and is harvested by means of miniature wind turbines and vibrations, using piezoelectric transduction. In both cases, the generated electric charge is stored in these capacitors. The performance of the organic capacitors are evaluated through their comparison with commercial capacitors. The results show that the voltage produced from the two energy harvesters was high enough to store the harvested energy in the organic capacitors. The charge and energy levels of the organic capacitors are also reported. The third part of this dissertation focuses on harvesting energy from a self-induced flutter of a thin composite beam. The composite beam consisted of an MFC patch bonded near the clamped end and placed vertically in the center of a wind tunnel test section. The self sustaining energy harvesting from the unimorph composite beam is exploited. The effects of different operational parameters including the optimum angle of attack, wind speed and load resistance are determined. / Ph. D.

Conductive paper materials consisting of conductive polymers and cellulose are promising for high-tech applications (energy storage and biosciences) due to outstanding aspects of environmental friendliness, mechanical flexibility, electrical conductivity and efficient electroactive behavior. Recently, a conductive composite paper material was developed by covering the individual nanofibers of cellulose from the green algae Cladophora with a polypyrrole (PPy) layer. The PPy-Cladophora cellulose composite paper is featured with high surface area (80 m2 g-1), electronic conductivity (~2 S cm-1), thin conductive layer (~50 nm) and easily up-scalable manufacturing process. This doctoral thesis reports the development of the PPy-Cladophora composite as an electrode material in electrochemically controlled solid phase ion-exchange of biomolecules and all-polymer based energy storage devices. First, electrochemical ion-exchange properties of the PPy-Cladophora cellulose composite were investigated in electrolytes containing three different types of anions, and it was found that smaller anions (nitrate and chloride) are more readily extracted by the composite than lager anions (p-toluene sulfonate). The influence of differently sized oxidants used during polymerization on the anion extraction capacity of the composite was also studied. The composites synthesized with two different oxidizing agents, i.e. iron (III) chloride and phosphomolybdic acid (PMo), were investigated for their ability to extract anions of different sizes. It was established that the number of absorbed ions was larger for the iron (III) chloride-synthesized sample than for the PMo-synthesized sample for all four electrolytes studied. Further, PPy-Cladophora cellulose composites have shown remarkable electrochemically controlled ion extraction capacities when investigated as a solid phase extraction material for batch-wise extraction and release of DNA oligomers. In addition, composite paper was also investigated as an electrode material in the symmetric non-metal based energy storage devices. The salt and paper based energy storage devices exhibited charge capacities (38−50 mAh g−1) with reasonable cycling stability, thereby opening new possibilities for the production of environmentally friendly, cost efficient, up-scalable and lightweight energy storage systems. Finally, micron-sized chopped carbon fibers (CCFs) were incorporated as additives to improve the charge-discharge rates of paper-based energy storage devices and to enhance the DNA release efficiency. The results showed the independent cell capacitances of ~60-70 F g-1 (upto current densities of 99 mA cm2) and also improved the efficiency of DNA release from 25 to 45%.

Master of Science / Department of Electrical and Computer Engineering / Noel Schulz / Many situations can cause a fault on a shipboard power system, especially in naval battleships. Batteries and ultra-capacitors are simulated to be backup energy storage devices (ESDs) to power the shipboard power system when an outage or damage occurs. Because ESDs have advantages such as guaranteed load leveling, good transient operation, and energy recovery during braking operation, they are commonly used for electrical ship applications. To fulfill these requirements, an energy management subsystem (EMS) with a specific control algorithm must connect ESDs to the dc link of the motor drive system. In this research, the real-time simulation of shipboard power system (SPS), bidirectional DC-DC converter, EMS, and ESDs are designed, implemented, and controlled on OPAL-RT system to test SPS survivability and ESD performance in various speed operations.

In this thesis, a test system is designed and implemented in order to evaluate the basic electrical performance and determine the parameters of ultracapacitors (UC). The implemented UC test system is based on power electronics converters and it is capable of charging and discharging the UC under test with predetermined current profiles. The charging operation is provided by a configuration involving the AC utility grid, a step-down transformer, a diode bridge, and a DC bus filter capacitor followed by a step-down DC-DC converter. The energy stored in the UC under test, as a result of the charging operation, is discharged to a resistor bank through a step-up DC-DC converter and a DC chopper structure. The charging and discharging current applied to the UC under test is provided by means of current mode control of power electronics converters. The control mechanism of the power electronics converters and the transition operations between the charging and discharging phases of the test system is realized via a microcontroller supported hardware structure. In the scope of the thesis study, a UC module composed of five serially connected UC cells is constructed. Constant current and constant power tests are applied to the constructed UC module. The performance of the implemented UC test system is investigated by means of computer simulations and experimental results. Further, basic electrical behaviour of the constructed UC module is evaluated and the parameters are extracted experimentally.

Electric double layer capacitors (EDLCs) are an important class of electrical energy storage devices which store energy in the form of electric double layers. The charging mechanism is highly reversible physical adsorption of ions into the porous electrodes, which empower these devices to show a remarkable power performance (15kW/kg) and greater life expectancy (> 1 million cycles). However, they store a small amount of energy (5Wh/kg) when compared with batteries. Optimization of the performance of EDLCs based on porous activated carbons is highly challenging due to complex charging process prevailing in the Nano pores of electrodes. Molecular simulations provide information at the molecular scale which in turn can be used to develop insights that can explain experimental results and design improved EDLCs. The conventional approach to simulate EDLCs places both the electrodes and electrolyte region in a single simulation box. With present day computers, however, this one-box method limits us to system sizes of the order of nanometres whereas the size of a typical EDLC is at least of the order of micrometres. To overcome this system size limitation, a Gibbs-ensemble based Monte Carlo (MC) method was recently developed, where the electrodes are simulated in a separate simulation boxes and each box is subjected to periodic boundary conditions in all the three directions. This allows us to eliminate the electrode-electrolyte interface. The simulation of the bulk electrolyte is avoided through the use of the grand canonical ensemble. The electrode atoms in the electrode are maintained at an equal constant electric potential likewise the case in a pure conductor with the use of the constant voltage ensemble. In this thesis, the Gibbs-ensemble based MC simulations are performed for an EDLC consisting of porous electrodes. The simulations are performed with aqueous electrolytes of type MX and DX2 (where M=Na+, K+; D=Ca+2; X=Cl , F ) for a wide variety of operating conditions. The water is modelled as a continuum background with a dielectric constant value of 30. The electrodes are silicon carbide-derived carbon, whose microstructure generated from reverse MC technique, is used in the simulations. The results from these simulations help us understand the charge storage mechanism, the effect of size and valence of ions on the performance of nonporous carbon based EDLCs when the hydration effects are indignant. The thesis first demonstrates the presence of finite size effects in the simulations performed with the one-box method for KCl electrolyte. The capacitance (ratio of the charged stored on the positive electrode to the voltage applied) values obtained for KCl electrolyte with the one-box method are significantly higher than the corresponding values obtained from the Gibbs-ensemble method. This shows the presence of finite size effects in the one-box method simulations and justices the use of the Gibbs-ensemble based method in our simulations. The fundamental characteristics of aqueous electrolytes in the EDLC are analyzed with the simulation results for KCl electrolyte. In agreement with experiments and modern mean held theory, the capacitance monotonically decreases with voltage (bell-shaped curve) due to overcrowding of ions near the electrode surface. The charge storage mechanism in both the electrodes is mainly a combination of countering (ions oppositely charged to that of the electrode) adsorption and ion exchange, where coins (ions identically charged to that of the electrode) are replaced with countering. However, at higher voltages, the mechanism is predominantly counter ion adsorption because of the scarcity of coins in the electrodes. The mechanism is preferentially more ion exchange for the positive electrode because of its relatively bulky countering, Cl . The shifting of mechanism towards counter ion adsorption at higher voltages and preferential ion exchange process for the positive electrode are in qualitative agreement with the recent experimental results. The constraint of equal electric potential on all the electrode atoms of the amorphous electrode in the simulations resulted in a non-uniform average charge distribution on the electrodes. It shows that the Gibbs-ensemble simulation approach can account for the polarization effects which arises due to a complex topology of the electrodes. In agreement with earlier experiments and simulation studies, the local structure analyses of the electrodes shows that the highly conned ions store charge more efficiently. On the application of voltage difference between the electrodes, the electrolyte ions move towards higher degree of con ned regions of the electrodes indicating the charging process involves local rearrangement and rescuing of electrolyte ions. The thesis also discusses the effect of temperature and bulk concentration on the performance of EDLCs. The Gibbs-ensemble based simulations are performed for the EDLC with varying temperature and bulk concentration for the KCl electrolyte independently. In agreement with the Guo -Chapman theory and experiments, the capacitance decreases with the temperature and increases with the bulk concentration. This is because the concentration of countering in the electrodes decreases with an increase in the temperature but increases with an increase in the bulk concentration. Lastly, the effect of ion size and valency on the performance of EDLCs is analyzed. The capacitance monotonically decreases with voltage (bell-shaped curve) for all the electrolytes, except for NaF, where a maximum is observed at a non-zero finite voltage (camel-shaped curve). The capacitances of NaCl and NaF are greater than that for KCl and KF, respectively. This is because the smaller Na+ ions have more accessibility to narrow con ned regions, where the charge storage efficiency is high. As expected, the capacitance for CaCl2 and CaF2 are highest among their monovalent counterparts, NaCl and KCl; NaF and KF, respectively. This is attributed to the relatively smaller double layer thickness of the bivalent Ca+2 ions. Interestingly, at higher voltages, the capacitance for the bivalent electrolytes approaches the capacitance for the monovalent electrolytes because the concentration of Ca+2 ions in the negative electrode increases sluggishly with voltage due to a strong electrostatic repulsion between Ca+2 ions.

Philosophiae Doctor - PhD (Chemistry) / Lithium ion capacitors are new and promising class of energy storage devices formed from a combination of lithium-ion battery electrode materials with those of supercapacitors. They exhibit better electrochemical properties in terms of energy and power densities than the above mentioned storage systems. In this work, lithium manganese oxide spinel (LiMn2O4; LMO) and lithium manganese phosphate (LiMnPO4; LMP) as well as their respective nickel-doped graphenised derivatives (G-LMNO and G-LMNP) were synthesized and each cathode material used to fabricate lithium ion capacitors in an electrochemical assembly that utilised activated carbon (AC) as the negative electrode and lithium sulphate electrolyte in a two-electrode system. The synthetic protocol for the preparation of the materials followed a simple solvothermal route with subsequent calcination at 500 - 800 ?C. The morphological, structural and electrochemical properties of the as prepared materials were thoroughly investigated through various characterisation techniques involving High resolution scanning electron microscopy (HRSEM), High resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), Small-angle X-ray scattering (SAXS), Electrochemical impedance spectroscopy (EIS), Cyclic voltammetry (CV) and Galvanostatic charge/discharge.