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Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains x, 165 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 163-165).

The current Li-ion technologies allow the popularity of Li-ion batteries as electrical energy storage for both mobile and stationary applications. The graphite-based anode is most commonly used in commercial Li-ion batteries. However, because lithium intercalation in graphite occurs very close to the redox potential of Li/Li+, accidental lithium plating is a known hazard capable of resulting in internal shorting, particularly when the battery is charged rapidly, requiring higher overpotentials to accomplish the Li-intercalation. Moreover, toward the next-generation battery, a growing interest is now on promising rechargeable Na-ion batteries. The main motivation for Na-ion alternative is that sodium is much more abundant and widely distributed on the earth’s crust than lithium. In the first part of this dissertation, we investigate safer, higher specific capacity anode materials for both Li-ion and Na-ion batteries. In a separated effort toward the efficient solar energy harvesting, the second part of the dissertation examines thin film photoanodes, active in the visible-light region, for photoelectrochemical water oxidation. This part also discusses in detail the synthesis, characterization, as well as the use of co-catalysts to improve the electrode’s photochemistry performance. The current Li-ion technologies allow the popularity of Li-ion batteries as electrical energy storage for both mobile and stationary applications. The graphite-based anode is most commonly used in commercial Li-ion batteries. However, because lithium intercalation in graphite occurs very close to the redox potential of Li/Li+, accidental lithium plating is a known hazard capable of resulting in internal shorting, particularly when the battery is charged rapidly, requiring higher overpotentials to accomplish the Li-intercalation. Moreover, toward the next-generation battery, a growing interest is now on promising rechargeable Na-ion batteries. The main motivation for Na-ion alternative is that sodium is much more abundant and widely distributed on the earth’s crust than lithium. In the first part of this dissertation, we investigate safer, higher specific capacity anode materials for both Li-ion and Na-ion batteries. In a separated effort toward the efficient solar energy harvesting, the second part of the dissertation examines thin film photoanodes, active in the visible-light region, for photoelectrochemical water oxidation. This part also discusses in detail the synthesis, characterization, as well as the use of co-catalysts to improve the electrode’s photochemistry performance.

The ever-increasing energy consumption and the environmental issues from the excessive rely on fossil fuels have triggered intensive research on the next generation power sources. Metal-air batteries, as one of the most promising technologies emerged, have attracted enormous attention due to its low cost, environmental benignity and high energy density. Among all types of metal-air batteries, Zn-air batteries in particular have tremendous potential for use as alternative energy storage primarily by the low-cost, abundance, low equilibrium potential, environmental benignity, a flat discharge voltage and a longer shell life. However, there are still issues in pertinent to the anode, electrolyte and cathode that remain to be overcome. In particular, the electrocatalyst at the cathode of a metal-air battery which catalyzes the electrochemistry reactions during charge and discharge of the cell plays the most crucial role for the successful commercialization of the metal-air technology. A series of studies from the carbon nanofibres to spinel cobalt oxide and perovskite lanthanum nickelate was conducted to explore the ORR/OER catalytic properties of those materials which lead to further investigations of the non-precious metal oxide/carbon hybrids as bifunctional catalysts. Introducing ORR active species such as nitrogen, sulfur, boron and phosphorus into high surface area carbon has been an effective strategy to fabricate high catalytic activity ORR electrocatalyst. Carbon nanofibre is an abundant, low cost and conductive material that has tremendous potential as ORR catalyst, especially via KOH activation and nitrogen-doping post-treatments. These two post-treatment methods serve as simplistic methodologies to enhance the carbon surface area and ORR catalytic activity of the pristine carbon nanofibres, respectively. The activated and nitrogen-doped carbon nanofibres demonstrated 26% of improved half-wave potential and 17% of increased limiting current density as a comparison to the pristine carbon nanofibre via RDE testing in alkaline electrolyte. To realize the catalytic activity of activated and nitrogen-doped carbon nanofibres in a more practical condition, they are further evaluated in Zn-air batteries. Polarization curves retrieved from Zn-air cell testing showed 75% higher voltage obtained by activated and nitrogen-doped carbon nanofibres than pristine carbon nanofibres at 70mAcm-2 current density. Structured oxides such as spinels and perovskites have been widely reported as ORR and OER catalyst in metal-air batteries. It is widely known that the properties of nanostructures are closely pertinent to their morphologies. The initial performance and durability of cubic Co3O4 synthesized from Feng et al and LaNiO3 from modified sol-gel method are tested in RDE system. After the durability testing, the ORR onset potential and limiting current density of cubic Co3O4 has decreased by 50% and 25%, respectively, whereas the OER limiting current density dropped significantly from ~15mAcm2 to almost zero current density. LaNiO3 with different particle sizes synthesized from modified sol-gel method was prepared and evaluated in RDE system. A particle size related performance can be clearly seen from the RDE results. The ORR limiting current of the lanthanum nickelate with smaller particle size (LNO-1) is higher than that of lanthanum nickelate with larger particle size (LNO-0) by 40% and the OER limiting current of LNO-1 is almost tripled that of LNO-0. With the previous experience on carbon material and structured oxides, two hybrid bifunctional catalysts were prepared and their performance was evaluated. cCo3O4/ExNG was made by physically mixing of cCo3O4 with ExNG with 1to 1 ratio. The hybrid showed enhanced bifunctional catalytic activities compared to each of its individual performance. Based on the voltammetry results, a significant positive shift (+0.16V) in ORR half-wave potential and tripled limiting current were observed in the case of the hybrid compared to the pure cobalt oxide. By combing cCo3O4 and ExNG, the OER limiting current of the hybrid exceeds that of cCo3O4 by ca. 33% and four-fold that of the ExNG. The kinetic current density at -0.4V for cCo3O4/ExNG is 15.9 mAcm-2 which is roughly 4 times the kinetic current density of the ExNG (3.8 mAcm-2) and over 10 times greater than that of cCo3O4 (1.1 mAcm-2). Electrochemical impedance spectroscopy showed that the charge transfer resistance of the hybrid is ca. one third of cCo3O4 and roughly only one half of ExNG which suggests a more efficient electrocatalysis of the hybrid on the air electrode than the other two. Mixing structured oxides with carbon material provides a simple method of fabricating bifunctional catalysts, however the interactions between those two materials are quite limited. In-situ synthesis of cCo3O4/MWCNT hybrid by chemically attaching cCo3O4to the acid-functionalized MWCNT is able to provide strong interactions between its components. Through RDE testing, the ORR activity of cCo3O4/MWCNT outperformed its individual component showing the highest onset potential (-0.15V) and current density (-2.91 mAcm-2 at -0.4V) with ~4 electron transfer pathway. Moreover, the MWCNT and cCo3O4 suffered from significant OER degradation after cycling (92% and 94%, respectively) whereas the hybrid material demonstrated an outstanding stability with only 15% of performance decrease, which is also far more superior to the physical mixture (30% higher current density). Among all the catalyst studied, cCo3O4/MWCNT has the highest performance and durability. The excellent performance of the hybrid warrants further in-depth research of non-precious metal oxide/carbon hybrids and the information presented in this thesis will create afoundation for future investigation towards high performance and durability bifunctional electrocatalysts for metal-air battery applications.

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Metal air battery has captured the spotlight recently as a promising class of sustainable energy storage for the future energy systems. Metal air batteries offer many attractive features such as high energy density, environmental benignity, as well as ease of fuel storage and handling. In addition, wide range of selection towards different metals exists where different energy capacity can be achieved via careful selection of different metals. The most energy dense systems of metal-air battery include lithium-air, aluminum-air and zinc-air. Despite the choice of metal electrode, oxygen reduction (ORR) occurs on the air electrode and oxidation occurs on the metal electrode. The oxidation of metal electrode is a relatively facile reaction compared to the ORR on the air electrode, making latter the limiting factor of the battery system. The sluggish ORR kinetics greatly affects the power output, efficiency, and lifetime of the metal air battery. One solution to this problem is the use of active, affordable and stable catalyst to promote the rate of ORR. Currently, platinum nanoparticles supported on conductive carbon (Pt/C) are the best catalyst for ORR. However, the prohibitively high cost and scarcity of platinum raise critical issues regarding the economic feasibility and sustainability of platinum-based catalysts. Cost reduction via the use of novel technologies can be achieved by two approaches. The first approach is to reduce platinum loading in the catalyst formulation. Alternatively platinum can be completely eliminated from the catalyst composition. The aim of this work is to identify and synthesize alternative catalysts for ORR toward metal air battery applications without the use of platinum re other precious metals (i.e., palladium, silver and gold). Non-precious metal catalysts (NPMC) have received immense international attentions owing to the enormous efforts in pursuit of novel battery and fuel cell technologies. Different types of NPMC such as transition metal alloys, transition metal or mixed metal oxides, chalcogenides have been investigated as potential contenders to precious metal catalysts. However, the performance and stability of these catalysts are still inferior in comparison. Nitrogen-doped carbon materials (NCM) are an emerging class of catalyst exhibiting great potential towards ORR catalysis. In comparison to the metal oxides, MCM show improved electrical conductivity. Furthermore, NCM exhibit higher activity compared to chalcogenides and transition metal alloys. Additional benefits of NCM include the abundance of carbon source and environmental benignity. Typical NCM catalyst is composed of pyrolyzed transition metal macrocycles supported by high surface area carbon. These materials have demonstrated excellent activity and stability. However, the degradation of these catalysts often involves the destruction of active sites containing the transition metal centre. To further improve the durability and mass transport of NCM catalyst, a novel class of ORR catalyst based on nitrogen-doped carbon nanotubes (NCNT) is investigated in a series of studies. The initial investigation focuses on the synthesis of highly active NCNT using different carbon-nitrogen precursors. This study investigated the effect of using cyclic hydrocarbon (pyridine) and aliphatic hydrocarbon (ethylenediamine) towards the formation and activity of NCNT. The innate structure of the cyclic hydrocarbon promotes the formation of NCNT to provide higher product yield; however, the aliphatic hydrocarbon promotes the formation of surface defects where the nitrogen atoms can be incorporated to form active sites for ORR. As a result, a significant increase in the ORR activity of 180 mV in half-wave potential is achieved when EDA was used as carbon-nitrogen precursor. In addition, three times higher limiting current density was observed for the NCNT synthesized from ethylenediamine. Based on the conclusion where highly active NCNT was produced from aliphatic hydrocarbon, similar carbon-nitrogen precursors with varying carbon to nitrogen ratio in the molecular structure (ethylenediamine, 1, 3-diaminopropane, 1, 4-diaminobutane) were adapted for the synthesis of NCNT. The investigation led to the conclusion that higher nitrogen to carbon ratio in the molecular structure of the precursors benefits the formation of active NCNT for ORR catalysis. The origin of such phenomena can be correlated with the higher relative nitrogen content of the resultant NCNT synthesized from aliphatic carbon precursor that provided greater nitrogen to carbon ratio. As the final nitrogen content increased in the molecular structure, the half-wave potential of the resultant NCNT towards ORR catalysis was increased by 120 mV. The significant improvement hints the critical role of nitrogen content towards ORR catalysis. To further confirm the correlation between the nitrogen content and ORR activity, another approach was used to control the final nitrogen content in the resultant NCNT. In the third investigation, a carbon-nitrogen precursor (pyridine) was mixed with a carbon precursor (ethanol) to form an admixture. The relative proportion of the two components of the admixture was varied to produce NCNT with different nitrogen content. By adopting this methodology, potential effect of different carbon-nitrogen precursors on the formation of NCNT can be eliminated since the same precursors were used for NCNT synthesis. Based on the electrochemical evaluations, the nitrogen content can be positively correlated to ORR activity. Among the NCNT samples, 41% higher limiting current density was achieved for 0.7 at. % increase in overall nitrogen content. Furthermore, the selectivity of the NCNT catalyst with higher nitrogen content favours the production of water molecule—the favourable product in metal-air battery by 43%. ORR catalyst is an outer-sphere electron transfer reaction whereby the reactants interact with the surface of catalysts. Consequently, the surface structure can be a determining factor towards the ORR activity of the NCNT in addition to the nitrogen content. In the forth investigation, the surface structure of NCNT was tailored to differentiate the ORR activity of smooth and rugged surface while controlling the overall nitrogen content to be similar. NCNT having different surface structures but similar nitrogen content (approximately 2.7 to 2.9 at. %) were successfully synthesized using different synthesis catalysts. Comparison of the two NCNT catalysts showing different surface structure resulted in a 130 mV increased in half-wave potential favouring the NCNT with more rugged surface structure. This study provided insights to the potential effects of synthesis catalyst towards directing the surface structure and the ORR activity of NCNT. Through a series of studies, the important parameters affecting the ORR performance of NCNT were elucidated and the most active NCNT catalyst synthesized was used for testing in a prototype zinc-air battery. The fifth study evaluated the performance of NCNT catalyst in different concentrations of alkaline electrolyte and at different battery voltage. An increase in the electrolyte’s alkaline strength improved the battery performance to a certain degree until the increasing viscosity impeded the performance of the battery system. The zinc-air battery employing NCNT as ORR catalyst produced a maximum battery power density of 69.5 mWcm-2 in 6M potassium hydroxide. The fifth study illustrated the great potential of NCNT towards the ORR catalysis for metal-air batteries. In combination, the series of investigations presented in this document provide a comprehensive study of a novel material and its application towards ORR catalysis in metal air batteries. Specifically, this report provides insights into the fundamentals of NCNT synthesis; the origins of ORR activity and the optimal operating conditions of NCNT in a prototype zinc-air battery. The excellent performance of NCNT warrants further studies of this material in greater details, and the information presented in this document will create a basis for future investigations towards ORR catalysis.

Wireless sensor network has been an area of interest among researchers. Designing a wireless sensor network involves multiple issues such as size and processing capacity of the sensors, number of the cluster heads, number of the base stations, routing protocols, battery of the nodes, layout of the system, etc. Battery is a critical factor, since sensor networks do not involve maintenance as they are situated in remote places. Hence the available battery must be utilized effectively to increase the efficiency. In our study we address issues associated with battery such that to increase the lifetime of the system. Existing standards for the sensors are implemented with each node having equal battery level `B' referred to as `Uniform system' in our study. Thus total amount of battery consumed by N nodes is `N * B'. In our approach we study the distribution of this `N * B' battery in non-uniform manner, referred as `Non-uniform system', such that each node would be allocated with different battery level depending upon its position and amount of information it receives and transmits. Initially we commence with the observation of the behavior of this approach on a chain of nodes. These nodes generate information at constant rate and transmit per cycle. We observed that there is a huge amount of increase in the lifetime as compared to lifetime of the uniform system. We step further in our experimentation by restricting the amount of battery each node can have and then quantizing it. Results indicate that only 3 levels of batteries instead of N, give us significant increase in the lifetime. These results validate our approach for practical implementation. We progressed by observing success of our approach on random topology where nodes are laid randomly in the area of experimentation. Approximately same increase in the lifetime as achieved initially without restricting battery levels can be achieved. Simulation results show that non-uniform system performs much better than uniform system. This approach of non uniform battery levels can be implemented in sensor networks such that system lives longer giving more throughput and thus increasing efficiency.

This PhD work is dedicated to the discovery and study of new cathode materials for lithium-ion batteries. To obtain new materials, a well-known strategy based on ion-exchanging alkali metals within stable crystalline frameworks was used. Ion-exchange procedures between sodium and lithium ions were performed on known sodiated materials, NaMnTiO4 with the Na0.44MnO2 structure and NaFeTiO4 and Na2Fe3-xSn2xSb1-xO8 (0 ≤ x ≤ 1) with the calcium-ferrite structure. A combination of Energy-Dispersive X-ray Spectroscopy (EDS), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), X-ray (XRD) and Neutron (NPD) diffractions was used to determine the crystal structure of the samples obtained via ion-exchange and confirmed that LiMnTiO4 and LiFeTiO4 and Li2Fe3-xSn2xSb1-xO8 (0 ≤ x ≤ 1) were obtained with a 1:1 ion-exchange between sodium and lithium. LiMnTiO4 has the orthorhombic Pbam space group, with a = 9.074(5), b = 24.97(1) and c = 2.899(2) Å. The shapes and dimensions of the channels are modified compared to NaMnTiO4, with displaced alkali metal positions and occupancies. LiMnTiO4 was cycled vs Li and up to 0.89 lithium ions can be reversibly inserted into the structure, with a discharge capacity of 137 mAh/g after 20 cycles at C/20 and room temperature. At 60°C, all the lithium is removed at the end of the first charge at C/20, with subsequent cycles showing reversible insertion of 1.06 Li-ions when cycled between 1.5 and 4.6 V. The electrochemistry of calcium-ferrite LiFeTiO4 and Li2Fe3SbO8 was investigated in half cells versus lithium and up to 0.63 and 1.35 lithium ions can be reversibly inserted into the structure after 50 cycles at a C/5 rate, respectively. LiFeTiO4 showed good cyclability with no capacity fade observed after the second cycle while Li2Fe3SbO8 exhibited a constant capacity fade with a 60 % capacity retention after the 50th cycle. Doping Li2Fe3SbO8 with tin reduces the capacity. However, the capacity retention is significantly enhanced. For Li2Fe2.5Sb0.5SnO8 after 20 cycles at C/5, the capacity is stable and comparable with that observed for Li2Fe3SbO8 after the same number of cycles. Using ion-exchange procedures has allowed new metastable materials to be obtained which have the potential to be used as cathodes in lithium-ion batteries. Doping these families of materials with different atoms has been shown to improve their electrochemical performance. Ex situ XRD was used to demonstrate that the original structures of LiMnTiO4, LiFeTiO4 and Li2Fe3SbO8 are retained during cycling. The volume change observed for Li2Fe3SbO8 upon delithiation was particularly noteworthy with a small decrease of 0.9 % at the end of charge when cycled at C/100 and room temperature, indicating structural stability upon lithium insertion/de-insertion.

abstract: Due to the increasing trend of electricity price for the future and the price reduction of solar electronics price led by the policy stimulus and the technological improvement, the residential distribution solar photovoltaic (PV) system’s market is prosperous. Excess energy can be sold back to the grid, however peak demand of a residential customer typically occurs in late afternoon/early evening when PV systems are not a productive. The solar PV system can provide residential customers sufficient energy during the daytime, even the exceeding energy can be sold back to the grid especially during the day with good sunlight, however, the peak demand of a regular family always appears during late afternoon and early evening which are not productive time for PV system. In this case, the PV customers only need the grid energy when other customers also need it the most. Because of the lower contribution of PV systems during times of peak demand, utilities are beginning to adjust rate structures to better align the bills paid by PV customers with the cost to the utility to serve those customers. Different rate structures include higher fixed charges, higher on-peak electricity prices, on-peak demand charges, or prices based on avoided costs. The demand charge and the on-peak energy charge significantly reduced the savings brought by the PV system. This will result in a longer the customer’s payback period. Eventually PV customers are not saving a lot in their electricity bill compare to those customers who do not own a PV system. A battery system is a promising technology that can improve monthly bill savings since a battery can store the solar energy and the off-peak grid energy and release it later during the on-peak hours. Sponsored by Salt River Project (SRP), a smart home model consists 1.35 kW PV panels, a 7.76 kWh lithium-ion battery and an adjustable resistive load bank was built on the roof of Engineering Research Center (ERC) building. For analysis, data was scaled up by 6/1.35 times to simulate a real residential PV setup. The testing data had been continuously recorded for more than one year (Aug.2014 - Oct.2015) and a battery charging strategy was developed based on those data. The work of this thesis deals with the idea of this charging strategy and the economic benefits this charging strategy can bring to the PV customers. Part of this research work has been wrote into a conference paper which is accepted by IEEE PES General Meeting 2016. A new and larger system has been installed on the roof with 6 kW PV modules and 6 kW output integrated electronics. This project will go on and the method come up by this thesis will be tested. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016