Nanostructured materials provide new and exciting approaches to the development of supercapacitor electrodes for high-performance electrochemical energy storage applications. One of the biggest challenges in materials science and engineering, however, is to prepare the nanomaterials with desirable characteristics and to engineer the structures in proper ways. This dissertation presents the successful preparation and application of very promising materials in the area of supercapacitor energy storage, including manganese dioxide and its composites, polyaniline and activated carbons. Attention has been paid to understanding their growth process and performance in supercapacitor devices. The morphological and electrochemical cycling effects, which contribute to the understanding of the energy storage mechanism of MnO2 based supercapacitors is thoroughly investigated. In addition, MnO2 based binary (MnO2-carbon nanocoils, MnO2-graphene) and ternary (MnO2-carbon nanotube-graphene) nanocomposites, as well as two novel electrodes (MnO2-carbon nanotube-textile and MnO2-carbon nanotube-sponge) have been studied as supercapacitor electrode materials, showing much improved electrochemical storage performance with good energy and power densities. Furthermore, a general chemical route was introduced to synthesize different conducting polymers and activated carbons by taking the MnO2 nanostructures as reactive templates. The electrochemical behaviors of the polyaniline and activated nanocarbon supercapacitors demonstrate the morphology-dependent enhancement of capacitance. Excellent energy and power densities were obtained from the template-derived polyaniline and activated carbon based supercapacitors, indicating the success of our proposed chemical route toward the preparation of high performance supercapacitor materials. The work discussed in this dissertation conclusively showed the significance of the preparation of desirable nanomaterials and the design of effective nanostructured electrodes for supercapacitor energy storage applications.

Renewable energy resources (RES) are becoming more popular for electricity generation due to their easy installation, flexibility, low cost, environmental compatibility, etc. However, their fluctuating nature is a major drawback, which decreases the power quality and makes them less trusty in the power system. To mitigate this problem, battery energy storage (BES) has been widely used with renewable energy sources. Because batteries are designed to handle “steady fluctuations” of power, the “sudden and peak” fluctuating power levels of renewable energy sources may cause shorter life spans for them, which may cause dramatic economic loss or negatively impact the power quality. Also, even though batteries have been used as a backup for RES, high power quality cannot be guaranteed when there is a rapid and peak fluctuations on source/load.

Research concentrated on the absorption, transformation, and storage of light energy is useful for the energy challenges faced by humanity. In particular, photocatalysis using solar energy to generate useful fuels has become a primary research goal in the drive to replace fossil fuels for the future. In this dissertation it is shown that poly-tetra(4-aminophenyl)porphyrin (pTAPP) can be oxidatively polymerized using a variety of methods, including electropolymerization, chemical oxidation, and interfacial polymerization and that pTAPP has photocatalytic ability to reduce O2 to H2O2 for a storable fuel. Organic conductive polymers such as pTAPP are attractive catalysts because of their high surface area and ability to coat electrodes. pTAPP in a mixed oxidation state is shown to have both its minimum charge transfer resistance as well as its minimum impedance to electronic conductivity in the film. The UV-vis-NIR absorption spectra of pTAPP with increased oxidative doping are similar to hyperporphyrin spectra, characteristic of a two-plus charge localized on a single porphyrin unit. This suggests the presence of a bipolaron on the individual porphyrin units, and thus a bipolaron conductivity mechanism has been proposed. pTAPP changes color depending on its oxidation state, and therefore is a promising material for electrochromic devices. A novel Pourbaix diagram was created as a means of illustrating the redox and protonation states of pTAPP as a function of changes in pH, applied potential, electrochromic behavior, and electronic conductivity. Both pTAPP and pCoTAPP were shown to be effective catalysts for the reduction of oxygen to hydrogen peroxide, with pCoTAPP a better catalyst than pTAPP. When pCoTAPP is irradiated, oxygen reduction occurs close to the thermodynamic potential, indicating a promising system for storage of solar energy.

This thesis makes a novel contribution to the state-of-the-art literature on EHD melting enhancement of PCMs showing the effects of electroconvection flow and solid extraction during the melting process. The details of the contribution made by this work have been disseminated in the form of three journal publications, which have been integrated into this sandwich Ph.D. thesis. / Latent heat thermal energy storage plays an important role in bridging the gap between the energy supply and consumer demands. The latent heat storage systems use phase change materials (PCMs) which are characterized by their high latent heat and therefore lead to higher energy densities. However, one major disadvantage of PCMs is their low thermal conductivities which affects the rates of charging and discharging. Electrohydrodynamics (EHD) offers an opportunity as an active heat transfer enhancement method which can significantly enhance the melting rates while being able to control the heat transfer as per the system’ needs with a very low power consumption. The application of EHD in two-phase solid liquid systems results in generating electroconvection flow in the liquid medium which increases the heat transfer coefficient and decreases the melting time. The main objective of the current work is to study the heat transfer enhancement and the role of EHD forces during the melting of phase change materials (PCMs) under constant temperature boundary conditions. There are two main investigations performed in the current study. First is experimentally studying the EHD melting enhancement of PCMs while applying high voltages through two rows of electrodes embedded inside the PCM. Moreover, in the experiments, solid extraction was investigated using high-speed imaging conducted at various locations with respect to the electrodes. In the second investigation, PCM melting in a rectangular cavity under the effect of EHD and constant temperature boundary conditions is studied numerically. The flow field, temperature field, and phase field are simulated during the melting process until a steady state condition is reached. Additionally, the effect of the applied voltage and temperature boundaries on the electroconvection flow is illustrated. Experimentally, the EHD melting enhancement of paraffin wax is examined under different applied DC voltage magnitudes and polarities, and different temperature gradients. In addition, the role of EHD forces was investigated by applying DC and AC square waves with different frequencies and offset values. The results showed that the melting enhancement increases with a nonlinear relation with voltages, wherein the maximum effective thermal conductivity was found to be 0.95 W/m-K at -10 kV in comparison with the value of 0.2 W/m-K for the pure liquid paraffin wax, with an enhancement ratio of 4.75. The Coulomb force was concluded to be the dominant EHD force in the study while the dielectrophoretic effect was negligible. Characterization of solid extraction was performed by measuring the intensity of extraction, and the size and velocity of dendrites after extraction at different applied voltages and temperature boundaries for different phase change materials having different mushy zone thickness. For paraffin wax, solid extraction was detected for all the applied DC voltages. Small dendrites were observed to be pulled out from the mushy zone melt front and rise upwards in a rotational manner. The extraction intensity was found to be high at locations of high Coulomb force near the electrodes. In addition, solid extraction measurements showed that the size and velocity of the extracted dendrites increase alongside the applied voltage while the velocity decreases at higher temperature boundaries. Finally, it was found that the existence of a large mushy zone results in higher solid extraction intensities. A numerical model was conducted using the finite element method to investigate the EHD melting of PCMs. In the model, the non-autonomous charge injection assumption is used with the Coulomb force being the only electrical body force considered. First, phase-change modeling is conducted to simulate the melting of paraffin wax without EHD under constant temperature boundary conditions until a steady-state condition is achieved. Next, the whole set of coupled EHD equations is introduced to the model to simulate the EHD melting process. The results revealed that two electroconvection cells were generated between each two successive electrodes in the liquid PCM. The EHD flow leads to the redistribution of the temperature field which enhances the heat transfer. EHD melting continues until a steady-state condition is regained after one hour of EHD time, at which point the enhancement ratio was found to be 2.33 at 6 kV. The influence of the applied voltages and temperature boundaries on the electroconvection flow showed that the fluid velocity increases significantly by increasing the voltage while it decreases under higher temperature gradients across the liquid region. This thesis makes a novel contribution to the state-of-the-art literature on EHD melting enhancement of PCMs showing the effects of electroconvection flow and solid extraction during the melting process. The details of the contribution made by this work have been disseminated in the form of three journal publications, which have been integrated into this sandwich Ph.D. thesis. / Thesis / Doctor of Philosophy (PhD)

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No description available.

Block copolymer-derived nanoporous materials are featured with microstructures defined by the microphase separation of constituent blocks, enabling various applications in energy storage. Dictated by the molecular weights and volume fractions of constituent blocks, the microphase separation forms nanoscale microstructures of 1-100 nm. Selective removal of a sacrificial phase produces nanopores with tailored pore width, continuity, and tortuosity. The remaining phase customizes the properties of resulting nanoporous materials, including specific surface area, electrical conductivity/insulation, and mechanical performance. Therefore, block copolymer-derived porous materials are felicitous for use in high-performance energy storage. This dissertation presents the utilization of block copolymers to derive nanoporous materials: i) high-modulus polyimide separators for lithium-metal batteries, and ii) high-surface-area carbon electrodes for fast-charging zinc-ion batteries. In lithium-metal batteries, the dendritic growth of lithium leads to deteriorating performance and severe safety concerns. Suppressing lithium dendrites is imperative to guarantee both high performance and safe cycling. Mesoporous polyimide separators are promising for dendrite suppression: i) the mesopores are smaller than the width of lithium dendrites, preventing lithium dendrites from penetrating the separator. ii) The high-modulus polyimide ceases the growth of lithium dendrites. Herein, this dissertation reports a mesoporous polyimide separator produced by thermalizing polylactide-b-polyimide-b-polylactide at 280 °C. The mesoporous polyimide separator exhibits a median pore width of 21 nm and a storage modulus of 1.8 GPa. When serving as a dendrite-suppressing separator in lithium-metal batteries, the mesoporous polyimide separator enables safe cycling for 500 hours at a current density of 4 mA/cm2. In zinc-ion batteries, developing cathodes compatible with fast charging remains a challenge. Conventional MnO2 gravel cathodes suffer from low electrical conductivity and slow ion (de-)insertion, resulting in poor recharging performance. In this dissertation, porous carbon fiber (PCF) supported MnO2 (PCF@MnO2), comprising nanometer-thick MnO2 deposited on block copolymer-derived PCF, serves as a fast-charging cathode. The high electrical conductivity of PCF and fast ion (de-)insertion in nanometer-thick MnO2 both contribute to a high rate capability. The PCF@MnO2 cathode, with a MnO2 loading of 59.1 wt%, achieves a MnO2-based specific capacity of 326 and 184 mAh/g at a current density of 0.1 and 1.0 A/g, respectively. This dissertation investigates approaches to utilizing block copolymers-derived nanoporous materials for high-performance energy storage. Those approaches are envisaged to inspire the design of block copolymer-derived nanoporous materials, and advance the development of "beyond Li-ion" energy storage. / Doctor of Philosophy / When we talk with friends on mobile phones, accomplish works on laptops, drive back home and see family's smiling faces under lamplights, we must have noticed that our daily life significantly relies on electrical energy. Although being predominantly employed in today's rechargeable energy storage, lithium-ion batteries using graphite anodes have approached their theoretical energy limits. We are expecting better-performance batteries for a more convenient life: to fully charge our phones faster, to use our laptops for a longer time, and to drive our electric cars for a further distance. Lithium-metal batteries and aqueous zinc-ion batteries stand out for "beyond lithium-ion" energy storage because they deliver more energy and charge faster. The commercialization of lithium-metal batteries and zinc-ion batteries may benefit from revolutionary porous materials derived from block copolymers. On one hand, lithium-metal batteries employ metallic lithium anodes, storing about 10 times of energy compared to equal-weight graphite anodes and allowing faster charging rates. However, the lithium-metal anodes grow needle-shaped dendrites during cycling. Those lithium dendrites traverse the battery separator through its large pores, causing internal short circuits and even fire hazards. Suppressing lithium dendrites is imperative for safe lithium-metal batteries. Stiff separators with small pores can suppress lithium dendrites. The small pores prevent lithium dendrites from traversing, and the stiff separators cease the dendritic growth. This dissertation introduces a dendrite-suppressing separator derived from block copolymers comprising stiff polyimide blocks and vulnerable blocks. When those block copolymers form films, the vulnerable blocks spontaneously disperse as a network embedded in the polyimide. Then, the vulnerable blocks are removed at elevated temperatures to create interconnected small pores. This porous polyimide separator suppresses lithium dendrites to allow safe cycling for 500 hours, surpassing today's separators which encounter short circuits within 60 hours. On the other hand, zinc-ion batteries require fast-charging cathodes for high charging rates. A fast-charging cathode demands both good electrical conductivity and fast ion insertion. Herein, this dissertation reports a porous carbon fiber supported MnO2 cathode. The block copolymers comprise a polyacrylonitrile block and a vulnerable block. The vulnerable blocks form a network dispersing in the polyacrylonitrile fibers. At elevated temperatures, polyacrylonitrile is converted to graphitic carbon fibers, and the vulnerable network decomposes to create interconnected pores. The porous carbon fibers afford a large surface area, allowing a high loading of MnO2 to deposit as nanometer-thick sheaths. The resulting cathode combines good electrical conductivity of porous carbon fibers and the fast ion insertion in thin MnO2 sheaths, therefore, exhibiting superior fast-charging performance. This dissertation reports the methods of using block copolymers to produce porous materials for high-performance batteries. We envisage those methods to inspire the design of block copolymer-derived porous materials, and advance the development of high-performance energy storage for a more convenient life.

A blackout is defined as the loss of electric power for a given period in a particular area. With increasing dependence on reliable electric power, the social and economic ramifications of blackouts are dire, negatively impacting the productivity, safety, and security of communities. To reduce blackout occurrence, power system planners incorporate redundancy and advanced controls to the grid to make it more adaptable to disturbances. However, adding redundant transmission lines is not only expensive, it is suboptimal in some contexts. While it is unattainable to have no blackout, it is possible and necessary to implement measures that minimize the likelihood and scale of these outages. This work proposes a solution that uses a microgrid with advanced energy storage and solar PV to mitigate blackouts in Kigali, the capital of Rwanda. A description and steady state analysis of major weaknesses in the Rwandan electric grid is presented. A microgrid application capable of islanding from the system is simulated in the steady state and shown to strengthen the system and decrease the likelihood of blackouts in Kigali. The composition of the microgrid is then designed, simulated, and optimized for technical and financial feasibility using the HOMER model. A microgrid that uses energy storage and solar PV is shown to not only be feasible, but also competitive with current costs of electricity in Rwanda. For comparison, different combinations that include diesel generation are also simulated. / Master of Science

Renewable Energy is by nature intermittent and matching the supply of energy to specific time dependent demand poses huge challenges. Energy storage is a useful tool in handling this temporal disparity, although except for regions very suitable for pumped hydroelectric storage schemes, it suffers from being technically difficult to implement and costly as a result. This study investigates the potential benefits offered by various scales of energy storage to different types of renewable energy generation. It also explores the economic drivers behind energy storage operating as part of an electricity spot market. A stochastic optimisation algorithm for determining the maximum possible arbitrage revenue available to energy storage devices is presented and schedule of operation of storage acting in this manner is analysed. The schedule of operation for maximising the revenue is compared to the schedule of operation for minimising the fuel cost to the network and it is demonstrated that because prices are more volatile than the demand which drives them, storage devices do not always act to decrease the fuel cost to the network. It is shown that storage behaving in the right manner can offer significant benefits to electricity systems, and increases the usage of base-load generation, reducing peak electricity demands and the need for expensive peaking plants. The value of storage also increases as the penetration of renewable energy generation increases, although the current electricity market framework is perhaps not the best way to encourage this behaviour. Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) is also identified as a theoretical storage option which deserves further scrutiny. Using thermodynamic modelling the efficiency of this type of system is estimated in the range of 63-67%, and we suggest that this may be increased closer to 73% by using direct contact heat exchangers rather than indirect contact heat exchangers (and a separate thermal fluid), as described in the currently available literature. However, dealing with large pressure ranges (leading to large variations in pressure ratios) encountered in the expansion process is a problematic area which will have to be resolved before this type of system can be constructed with “off-the-shelf” components. Some small scale experiments are used to gain valuable insights into a AA-CAES system. While these suffer from a very low overall efficiency, they highlight the effect of variable pressure ratio on expander efficiency. We conclude that AA-CAES is thermodynamically sound and will be achieved one of two ways: either through the construction of expanders that can work with high efficiency over large pressure ratios, or by resolving the engineering issues with maintaining a constant storage pressure.

Many new technologies are being introduced to the electrical power grid at the distribution voltage level. These technologies include electric vehicles (EVs), distributed generation, and battery energy storage systems (BESS) This thesis investigates how these various technologies can be harmoniously integrated into the electric grid. Therefore, a modeling environment that can simulate scenarios involving the above technologies in durations from hours to years was created. This modeling system is modular so that any feeder configuration can be simulated by the user and each module has individual user defined parameters or curves that define their operation. Optimum economic dispatch, stability enhancement, renewable generation smoothing, and peak-shaving algorithms were implemented into the modeling environment. With the use of the built in algorithms, or custom input, the simulation tool produces the necessary electrical and economic values to fully evaluate the system’s feasibility. Other algorithms created include renewable generation smoothing and stability enhancement.