PhD, University of Cincinnati, 2017, Engineering and Applied Science: Chemical Engineering

The redox flow batteries (RFBs) are a type of energy storage device that has gained tremendous interest for renewable power systems. However, commercialization of RFBs are largely limited by the inefficiencies of the existing ion separators, which are key component determining the battery efficiency, lifetime, and cost-effectiveness. The main goal of this dissertation research is to investigate porous inorganic membranes for proton-selective ion transport and conduction that are relevant to RFB operations. The research has been focused on the Vycor porous glass (VPG; Corning Co.) membrane and Al-containing MFI-type zeolite membrane. Experimental studies have demonstrated that both the VPG and ZSM-5 membranes possess excellent resistance to concentrated acid solutions, immunity to strong oxidizing environments, and structural stability in the aggressive solutions even at elevated temperature (45oC). However, the mesoporous VPG membrane, with relatively big pore size (dp ~4 nm), nonionic surface, and large thickness (500 µm), exhibits lower proton transport selectivity against vanadium ionsand higher area specific resistance (ASR) than the Nafion-117 membrane (DuPont), a benchmark ion separator for RFBs. Thus, the VPG membrane leads to lower efficiency in the VRFB than the Nafion membrane. Nevertheless, after operating at high temperature (45oC), the VPG equipped VRFB has shown a much smaller permanent loss in energy efficiency (EE) than that with the Nafion membrane. It has also been revealed that the VPG membrane is not vulnerable to surface contamination by metal ion sorption and structure damage at elevated temperature, which have been observed on the Nafion membrane. However, the mesoporous glass membrane due to its high ASR and low proton selectivity, which is not expected to provide high performance in the RFBs, especially for those using different metal ions in the positive and negative electrolyte solutions because of crossover contaminations. To address th (open full item for complete abstract)

Committee: Junhang Dong Ph.D. (Committee Chair); Anastasios Angelopoulos Ph.D. (Committee Member); Woo Kyun Kim Ph.D. (Committee Member); Peter Panagiotis Smirniotis Ph.D. (Committee Member) Subjects: Chemical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2018, Chemical Engineering

Inexpensive and scalable energy storage is necessary for the transition to a cleaner, more sustainable, electricity grid. The Acid-Base Energy Storage System (ABESS) utilizes an extremely inexpensive, safe, and abundant electrolyte, can be deployed anywhere without geographical constraints, and is predicted to be economical at very large energy storage capacities and long discharge times. The ABESS stores energy by utilizing the potential difference created by a proton (H+) concentration gradient in a saltwater electrolyte. The coulombic efficiency (ηC ) of an ABESS is unknown and it is crucial to understand for further development. In this thesis, the mass transport of the active species through Nafion® was measured and modeled in the charging of an ABESS under a high salt environment to determine ηC limitations. A macro-homogeneous model based on dilute solution theory utilizing Nernst-Planck equations was developed to relate ηC to the current density of an ABESS during charging. Effective diffusivities and transference numbers of sodium and active species under various electrolyte conditions were experimentally determined and reported for an ABESS operating with a concentrated saltwater electrolyte and a Nafion® separator. Using a Nafion®-212 membrane and a saturated sodium sulfate electrolyte at room temperature (∼1.5M Na2SO4 at 22°C ± 1.0°C), a maximum ηC of 86.7% ± 2.5% was measured during charging at 100 mA/cm2 up to a concentration of 0.5N Acid/Base in the respective reservoirs. These are promising results and show that a full battery will be able to achieve a 70% - 75% overall energy efficiency, comparable to other flow battery technologies.

Committee: Jesse Wainright Dr. (Advisor); Robert Savinell Dr. (Committee Member); Christine Duval Dr. (Committee Member) Subjects: Alternative Energy; Chemical Engineering; Energy; Engineering

Doctor of Philosophy, The Ohio State University, 2018, Chemistry

With increasing energy demand and adverse effects of CO2 emissions, a future dependent of fossil fuels becomes more problematic. A source of clean and renewable energy is necessary to sustain further economic growth. Therefore, research into converting and storing solar energy has become an area of increased interest. Due to the intermittent nature of sunlight, storage of solar energy becomes as important as its conversion. This dissertation covers two strategies to overcome these challenges, (1) development of next generation large scale batteries that can store solar energy for use at a later time and (2) Integration of the two functions into an all-in-one device which can offer simultaneous solar energy conversion and storage. A promising new technology called potassium-oxygen batteries have the potential to meet the requirements of large scale energy storage and have high theoretical energy densities up to 4 times that of current lithium ion batteries at a much lower cost. The potassium metal anode has been identified as the largest limitation of this technology. Therefore, development of new potassium alloy anode materials or novel electrolytes that stabilize the potassium metal are two strategies to improve the safety and stability of the battery. Using electrochemical measurements and x-ray diffraction, a crystalline K3Sb alloy can undergo reversible electron storage for many cycles, resulting in a stable anode for potassium-oxygen batteries. Additionally, synthetic tuning of the electrolyte allows for highly concentrated electrolytes which result in a stabilized potassium metal interface. These two combinations make the potassium-oxygen battery a more commercially viable option. The second strategy to promote the use of renewable energy is development of a solar redox flow battery that can offer simultaneous solar energy conversion and storage. These devices are based on the direct integration of a photoelectrode into a redox flow battery. Under illumi (open full item for complete abstract)

Committee: Yiying Wu Dr. (Advisor); Joshua Goldberger Dr. (Committee Member); Anne Co Dr. (Committee Member); Heather Chandler Dr. (Committee Member) Subjects: Chemistry; Energy

Master of Science in Polymer Engineering, University of Akron, 2025, Polymer Science

Redox flow batteries (RFBs) are a promising solution for scalable energy storage, enhancing grid stability and renewable energy integration. Using liquid electrolytes, they allow independent scaling of power and energy capacity for flexible design and long lifetimes. Iron-based catholytes offer a cost-effective, sustainable alternative, but challenges remain in improving energy density, cycle life, and efficiency. This study explores iron coordination complexes to enhance solubility and stability. Recent research achieved a nearly 3-fold solubility increase over ferrocyanide without redox potential loss. Sodium-ion exchange electrolytes enabled stable operation at 1.27 V, with 90.58% capacity retention over 1800 cycles at 30 mA/cm² and near 100% coulombic efficiency. These advancements support the development of efficient, low-cost RFBs for sustainable energy storage.

Committee: Yu Zhu (Advisor); Steven Chuang (Committee Member) Subjects: Chemical Engineering; Chemistry; Energy; Materials Science

Doctor of Philosophy, Case Western Reserve University, 2024, Chemical Engineering

Lowering energy-related CO2 emissions of the U.S. requires the implementation of renewable energy sources to generate electricity. These sources, e.g. solar and wind power, are intermittent in their output, necessitating some form of grid-scale energy storage. Redox flow batteries, particularly hybrid flow batteries based on zinc (Zn), are a highly attractive solution due to their high energy density, scalability, earth-abundance of Zn, and usage of safer aqueous electrolytes as opposed to flammable organics. However, Zn has notable problems such as forming dendrites during high-rate deposition and spontaneous corrosion in acidic and alkaline electrolytes leading to substantial self-discharge of a battery over time. To address these issues, significant research has been conducted on electrolyte additives that can suppress dendrite formation and prevent corrosion, but many of these conventional additives also polarize the electrode and harm battery energy-efficiency. In the present work, a novel additive, benzyldimethylhexadecylammonium chloride (BDAC), is shown to markedly suppress Zn corrosion (battery self-discharge) rate in a pH = 3 ZnSO4 medium without harming (i.e., by minimizing overpotential losses) the high-rate deposition or stripping performance of Zn. Cyclic voltammetry (CV) measurements show BDAC induces hysteresis, where the electrode can either exhibit passivity or electrochemical activity at a given electrode potential depending on the scan direction. The hysteresis is a result of complex surface adsorption and deactivation behavior of BDAC on Zn. An additive adsorption-deactivation model is proposed which captures above behavior and shows that, at low current densities (i.e. low BDAC deactivation rates), the electrode surface tends towards full additive coverage while, at higher deposition or stripping rates (i.e. rapid BDAC deactivation), the electrode surface tends towards a coverage depending on the additive's adsorption and deactivatio (open full item for complete abstract)

Committee: Rohan Akolkar (Committee Chair); Robert Warburton (Committee Member); Jesse Wainright (Committee Member); Alp Sehirlioglu (Committee Member) Subjects: Chemical Engineering

Master of Science, The Ohio State University, 2024, Chemistry

With sustainable energy storage at the forefront of global concerns, the development of high-performance, long-lasting battery systems is of paramount importance. The first chapter of this thesis explores polymerization techniques for synthesizing tetrazine-based polymers as sustainable cathode materials for aqueous Zn-ion batteries. Understanding the impact of polymerization on tetrazine electrode materials has interesting implications for the overall adoption of the tetrazine motif in energy storage. The second chapter of this thesis investigates the incorporation of nitrogen oxide gases in Na batteries. The incorporation of these gases promises to surpass cell potentials and reversibility seen in conventional Na-O2 or Na-CO2 batteries. By harnessing the unique properties of nitrogen oxides, this research aims to markedly enhance battery energy output, contributing to the advancement of sustainable energy technologies.

Committee: Yiying Wu (Committee Member); Shiyu Zhang (Advisor) Subjects: Chemical Engineering; Chemistry; Energy

Doctor of Philosophy, The Ohio State University, 2023, Chemistry

As the demand of electricity has increased and will increase continuously, the sustainable energy sources are in need. The major source of electricity, at least for now, is fossil fuel which generates carbon dioxide upon consumption. Carbon dioxide is one of the most well-known greenhouse gases that contribute to climate change. Thus, renewable energy sources must be found to reduce carbon dioxide emissions. Renewable energy, such as solar and wind, are emission-free, renewable, and replenishable. Unfortunately, geographical limitations and temporal fluctuations hinder their usage as energy sources. To maximize the utilization of such renewables, stationary storage devices may be utilized. With accessible storage capacity, it is possible to store energy when or where it is available and utilize it when it is required. Chemists are responsible for identifying and developing safe, economical, and sustainable technologies for grid-scale energy storage systems. Redox flow batteries (RFBs) are one of promising candidates for grid-scale storage systems which is scalable due to the decoupled relationship between the size of electrodes and the capacity. Since the electric energy is being stored in the solution containing redox species, increasing the volume of the solution will directly increase the capacity of the solution. However, the energy density of RBFs is relatively low compared to solid-state batteries such as Li-ion batteries. To improve the energy density of RFBs, redox-targeting flow batteries (RTFBs) have been developed where the additional redox active solids provide energy boost without increasing concentration or addition of solution. In the RFTBs, the redox species in solution undergoes electron transfer at the electrodes and sequentially undergo remote electron transfer with the solids. The remote electron transfer process is called redox-targeting reaction. In terms of combinations of the redox species in solution and solid materials, there are two po (open full item for complete abstract)

Committee: Christo Sevov (Advisor); Yiying Wu (Committee Member); Christopher Hadad (Committee Member) Subjects: Chemistry

Doctor of Philosophy, Case Western Reserve University, 2022, Chemical Engineering

Energy storage solutions are becoming increasingly necessary to enable wider penetration of renewable but intermittent sources of electricity such as wind and solar. Redox flow batteries (RFBs) offer a versatile solution to this problem due to their scalable nature provided a suitable electrolyte and redox chemistry system can be developed. To date no RFB system has been widely utilized due to key drawbacks. Aqueous electrolytes are limited in energy density by the electrolysis of water limiting the maximum operating voltage of any redox couple and by solubility of active species (limits near 2 M). Organic solvents, such as acetonitrile, often have a much larger stable electrochemical window but are often expensive and highly volatile making them dangerous to work with while still incurring solubility issues. Deep eutectic solvent (DES) electrolytes, offer unique advantages. They consist of hydrogen bond donor/acceptor pairs and often offer larger electrochemical windows than traditional aqueous electrolyte systems with lower vapor pressure than other non-aqueous alternatives. They contain a large concentration of charge carries and have the potential to be high energy density electrolytes. When paired with redox organic species it is possible to tune both the electrolyte and redox actives to obtain desirable electrochemical properties such as solubility of active species, kinetic and transport behaviors as well as redox potential In this work, tools and understanding are developed to predict the impact of molecular structure on desirable electrochemical properties such as solubility, stability, and redox behavior in hydrogen bonding electrolyte systems. Electrochemical decomposition of ethaline was investigated. Stability was determined to be limited by the presence or primary alcohols at both the anode and cathode. An alternative tertiary alcohol DES based on this result was found to have increased stability. The electrochemical behavior of several redox organ (open full item for complete abstract)

Committee: Robert Savinell (Committee Chair); Burcu Gurkan (Committee Member); Clemens Burda (Committee Member); Emily Pentzer (Committee Member); Jesse Wainright (Committee Member) Subjects: Chemical Engineering

PhD, University of Cincinnati, 2022, Arts and Sciences: Chemistry

Redox flow batteries (RFBs) are an attractive technology for large-scale energy storage due to their independent control over energy and power. However, the practical application of RFBs is generally restricted by low energy density, inferior power density, and insufficient cyclability. While remarkable progress was made on inorganic material-based RFBs, organic redox flow batteries, where organic compounds serve as redox-active materials, have recently attracted enormous attention because of their molecular diversity, structure designability, and low cost. The recent progress on organic redox-active materials, ranging from small molecules to polymers in aqueous and non-aqueous media, was reviewed. Particularly, the function-oriented molecular design of organic redox-active materials was presented. Finally, technological challenges and prospective research possibilities of organic redox-active materials in advanced large-scale RFBs were discussed. In this study, two viologen analogs with poly(ethylene glycol) (PEG) tails were designed as anolytes for non-aqueous RFBs. The PEGylation of viologen not only enhances the solubility in acetonitrile but also increases the overall molecular size for alleviated crossover. In addition, a composite nanoporous aramid nanofiber separator, which allows the permeation of supporting ions while inhibiting the crossover of the designer viologens, was developed using a scalable doctor-blading method. Paired with ferrocene, the full organic material-based RFB presents excellent cyclability (500 cycles) with a retention capacity per cycle of 99.93% and an average Coulombic efficiency of 99.3% at a current density of 2.0 mA/cm2. The high-performance of the PEGylated viologen validates the potential of the PEGylation strategy for enhanced organic material-based non-aqueous RFBs. We also investigated an evolutionary design of a set of bipyridines and their analogs as anolytes and examined their performance in full-flow batteries. Us (open full item for complete abstract)

Committee: Jianbing Jiang Ph.D. (Committee Member); Peng Zhang Ph.D. (Committee Member); David Smithrud Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2022, Chemistry

Ever-increasing energy consumption and rising public awareness for environmental protection require the development of new technologies for renewable energy conversion and storage. The renewable energy, abundant but intermittent, is usually stored in stable chemicals that can be easily converted back to electrical energy. This process is similar to how Nature harvests and utilizes solar energy through photosynthesis and respiration. For energy conversion, one of the major technologies is fuel cells. A Fuel cell is an electrochemical device that converts chemical energy in fuels directly into electrical energy. A fuel cell separates a combustion reaction into two half-reactions (fuel oxidation and oxygen reduction), and these two half-reactions occur in two physically separated chambers. In commercialized fuel cells, both reactions require platinum catalysts. Oxygen reduction reaction requires large amounts of platinum catalysts to achieve high current density. Therefore, developing alternative, cheap catalysts for ORR is important for lowering the price of fuel cells. In nature, life-sustaining ORR is catalyzed by multicopper oxidases (MCOs), where O2 is captured and reduced at a tricopper cluster. MCOs are a group of enzymes which can selectively catalyze the reduction of oxygen to H2O with a high turnover frequency (560 s-1). In Chapter 1 and Chapter 2, a biomimetic tricopper complex, resembling the active site in multicopper oxidases (MCOs), was developed to understand how nature employs tricopper clusters to catalyze ORR at near-zero overpotential. In order to mimic MCO's ability to reversibly store and deliver multiple electrons, a fully encapsulated tricopper complex was synthesized. Site isolation and intramolecular proton transfer site are further shown to be the two critical factors in lowering the overpotential of oxygen reduction reaction. Our work represents a significant step toward inexpensive and efficient copper catalysts for ORR. Another major tec (open full item for complete abstract)

Committee: Casey Wade (Committee Member); Psaras McGrier (Committee Member); Jovica Badjic (Committee Member); Shiyu Zhang (Advisor) Subjects: Chemistry

Doctor of Philosophy, University of Akron, 2022, Polymer Science

The limited availability of a high-performance catholyte and anolyte has hindered development of aqueous organic redox flow batteries (AORFB) for large-scale energy storage. In this work, a commercial available dye material was modified and evaluated in aqueous organic redox flow battery as anolyte. The desalted Basic Red 5 dye molecules (d-BR5) exhibited reasonably solubility in acidic supporting electrolyte and stable redox performance. The cell of d-BR5 and (Ce(CH3SO3)3) exhibited an operating voltage ~ 1.4 V, with 99.9% capacity retention after 200 cycles. The results indicated that organic dye molecules could be potential low cost active materials for aqueous organic redox flow battery. Furthermore, a symmetrybreaking design of iron complexes with 2,2'-bipyridine-4,4'-dicarboxylic (Dcbpy) acid and cyanide ligands was reported. By introducing two ligands to the metal center, the complex compounds (M4[FeII(Dcbpy)2(CN)2], M = Na, K) exhibited up to 4.2 times higher solubility (1.22 M) than M4[FeII(Dcbpy)3] and a 50% increase in potential compared with ferrocyanide. The AORFBs with 0.1 M Na4[FeII(Dcbpy)2(CN)2] as catholyte were demonstrated for 6000 cycles with capacity fading rate of 0.00158% per cycle (0.217% per day). Even at a concentration near the solubility limit (1 M Na4[FeII(Dcbpy)2(CN)2]), the flow battery exhibited capacity fading rate of 0.008% per cycle (0.25% per day) in the first 400 cycles. The AORFB cell with a nearly 1:1 catholyte:anolyte electron ratio achieved a cell voltage of 1.2 V and an energy density of 12.5 Wh/L. A solid-state electrolyte is crucial for all solid-state lithium metal batteries. A fluorinated crosslinkable polymer electrolyte with superionic conductivity and high-voltage stability is reported in this work. The high-voltage tolerance of the fluorinated polymer make the solid electrolyte suitable for high voltage cathodes such as lithium nickel cobalt aluminum oxide (NCA). By using ternary phase diagram, the crosslinked po (open full item for complete abstract)

Committee: Yu Zhu (Advisor); Steven S.C. Chuang (Committee Co-Chair); Zhenmeng Peng (Committee Member); Kevin Cavicchi (Committee Member); Chunming Liu (Committee Member) Subjects: Chemistry; Energy; Engineering

Doctor of Philosophy, University of Akron, 2020, Polymer Science

Organic materials have been extensively studied for electronics and energy storage techniques, due to their abundant sources, processability and structure tunability. In the past two decades, π-conjugated organic molecules have been widely investigated for semiconductors in organic field effect transistors (OFETs). In general instances, the efficiency of charge transport in π-conjugated molecules significantly determined the performance of the organic semiconductors in field effect transistors (FETs). As the charge transport in organic materials are correlated to their molecule assembly, it is crucial to understand the relationship between molecular structure and electronic property. Typically, organic semiconductors are comprised of π-conjugated molecules, among which the π- π interactions contribute to the assembly. Hydrogen bonding, as another strong intermolecular interaction, has also been recognized to promote the molecular packing. Herein, in this dissertation, chapter II is focused on the study about the molecular packing and electronic properties after the formation of hydrogen bonding in selected organic molecules. Additionally, except for the semiconductors, the tunability of organic molecules is also able to afford desired electrochemical properties for redox flow batteries (RFBs). Redox flow battery is a type of energy storage technique with a unique feature of separated energy and power. In other words, the electrolyte that contributes to the energy is stored away from the cell component, rendering high operation safety and adjustable energy storage capacity. Commercial RFBs, such as the all-vanadium RFBs, use inorganic metal ions as electrolytes for the energy storage. Those systems are limited by the high cost of metal sources and severe electrolyte crossover during cycling. A viable way to promote the development of RFBs is to introduce aqueous soluble organic (ASO) redox active materials, because of their tunable electrochemical properties and s (open full item for complete abstract)

Committee: Yu Zhu PhD (Advisor); Steven S.C. Chuang PhD (Committee Chair); Tianbo Liu PhD (Committee Member); Chunming Liu PhD (Committee Member); Weinan Xu PhD (Committee Member) Subjects: Chemistry; Energy

Doctor of Philosophy, University of Akron, 2019, Chemistry

Electrochemical characterization is required in a wide range of applications. It can be applied to electrocatalysis and corrosion studies, energy usage of organisms, and energy storage in batteries. The purpose of this research is two-fold: development of an electrochemical characterization technique which can be used at elevated temperatures; electrochemical characterization of a series of ferrocene derivatives for redox flow battery (RFB) application. Electrochemical measurements at elevated temperatures have attracted considerable attention, and a technique called Hot-Tip Scanning Electrochemical Microscopy (HT-SECM) has been developed in this study. In this technique, heating is achieved by applying alternating current (ac) waveform (~100 MHz, several Vrms) between the tip sensor and counter electrodes. Various HT-SECM operation modes were discussed. The tip currents were collected as the tip was brought close to the substrate at room temperature and when the ac heating was applied. Numerical simulations performed in COMSOL Multiphysics support the experimental findings, and additional analytical approximations were developed that could be used to predict the faradaic response in HT-SECM experiments. A good understanding of HT-SECM was achieved, both experimentally and theoretically, suggesting that this methodology could be applied to investigate electrode kinetics under the conditions of elevated temperature and increased rate of mass transfer. The second part of this research is the electrochemical characterization of ferrocene derivatives as new molecular strategies for RFB applications. Ferrocene has very reversible electrochemistry but low solubility in aqueous solutions. The electrochemistry of four ferrocene derivative anions were compared to that of the (ferrocenemethyl)trimethylammonium cation, which has been reported as a promising catholyte in aqueous RFB. It was found that solvent effects play a significant role in the performance of these compoun (open full item for complete abstract)

Committee: Aliaksei Boika PhD (Advisor); Chrys Wesdemiotis PhD (Committee Member); Yi Pang PhD (Committee Member); Adam Smith PhD (Committee Member); Rajeev Gupta PhD (Committee Member) Subjects: Analytical Chemistry; Chemistry; Energy; Inorganic Chemistry

Master of Sciences (Engineering), Case Western Reserve University, 2017, Chemical Engineering

Nafion, as the benchmark proton exchange membrane, has been used in all vanadium flow battery applications in large scale. However, it is expensive and known to have high permeability to vanadium species. Hereby, we proposed and investigated sulfonated poly ether ether sulfone (SPEES) hydrocarbon polymer doped by metal organic frameworks (MOFs) material ZIF-8, which is a family of MOFs with zeolite topology, as an alternative for Nafion membrane. In this project, firstly, SPEES membrane has been successfully synthesized and doped with self-synthesized MOFs material ZIF-8. Secondly, we investigated its electrochemical properties including proton conductivity and VO2+ permeability as well as its physicochemical properties including degree of sulfonation, ion exchange capacitor and water uptake with doping different content of ZIF-8. Lastly, we evaluate its feasibility and overall performance through cycling the all vanadium redox flow battery single cell with a membrane assembled inside. The results show the conductivity of SPEES/ZIF-8 membrane increases with the in crease of ZIF-8. The SPEES membrane with 3 wt% ZIF-8 exhibits the best conductivity (~0.19 S/cm), higher than Nafion 117(~0.095 S/cm) at 20 C in 1 M sulfuric acid. Moreover, the results of permeability measurement show adding more ZIF-8 lowers the permeability to VO2+. The SPEES membrane with 3 wt% ZIF-8 exhibits the best permeability to VO2+ (~1.35 × 10-8 cm2/s), which is lower than Nafion 117 (~6.09 ×10-8cm2/s). In the vanadium redox flow battery (VRB) cycling performance test, with 1.5 M V2+/V3+ in 3 M sulfuric acid as negative electrolyte and 1.5 M VO2+/VO+2 in 3M sulfuric acid as positive electrolyte, SPEES/ZIF-8 exhibits higher energy efficiency (71.0 %) as compared to Nafion 117 (68.1 %), higher voltage efficiency (77.2 %) as compared to Nafion 117 (73.7 %), while having nearly the same coulombic efficiency (~ 92%) at 40 mA/cm2. These results indicate that SPEES/ZIF-8 membrane is a promising al (open full item for complete abstract)

Committee: Robert Savinell (Advisor); Jesse Wainright (Committee Member); Chung-Chiun Liu (Committee Member) Subjects: Chemical Engineering; Energy

PhD, University of Cincinnati, 2016, Engineering and Applied Science: Chemical Engineering

Electrostatic Layer-by-Layer (LbL) assembly of nanoplatelets of stacked graphene sheets and bismuth metal nanoparticles having negative surface charge on cationic polymer binder was investigated as an electrode fabrication method. The bismuth nanoparticles were synthesized utilizing a novel aqueous-based autoreduction scheme wherein SnCl2serves as both reducing and stabilizing agent. Correlation of well-defined electrode nanostructure to fundamental electrocatalytic activity was evaluated using Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS), Rotating Disk Electrode (RDE), Cyclic Voltammetry (CV), and Electrochemical Impedance Spectroscopy (EIS). LbL assembly was found to be a facile method of obtaining large electrochemically active mass-specific surface areas for the positive VO2+/VO 2+ and the negative V3+/V 2+ redox reactions crucial to Vanadium Redox Flow Battery (VRFB) application for large-scale energy storage. Redox exchange currents obtained using RDE were found to increase with the number of carbon nanoplatelet layers deposited. This process thereby provides a convenient means by which energy storage can be systematically scaled to differing power requirements. LbL assemblies for the positive VO 2+/VO 2+ electrode consisted of horizontally oriented stacked graphene nanoplatelets deposited onto cationic polymer binder that yielded a constant exchange current density, i0, of 3.36 mA cm-2 per layer. Nanoplatelet agglomeration did not impact the electrochemically active area with the deposition of successive layers. In the case of the negative V 3+/V 2+ redox reaction, layered structures consisted of co-adsorbed bismuth metal and stacked graphene nanoplatelets in horizontal orientations exhibited i 0 that increased from 35.81 mA cm-2 for 4 layers to 52.63 mA cm-2 for 20 layers. Increasing CV currents at peak potential with number of layers were also observed on more commercially viable bipolar substrate materials. Identically orien (open full item for complete abstract)

Committee: Anastasios Angelopoulos Ph.D. (Committee Chair); Junhang Dong Ph.D. (Committee Member); Sundaram Murali Meenakshi Ph.D. (Committee Member); Vesselin Shanov Ph.D. (Committee Member) Subjects: Chemical Engineering

PhD, University of Cincinnati, 2014, Engineering and Applied Science: Chemical Engineering

Microporous zeolite membranes have been widely studied for molecular separations based on size exclusion or preferential adsorption-diffusion mechanisms. The MFI-type zeolite membranes were also demonstrated for brine water desalination by molecular sieving effect. In this research, the pure silica MFI-type zeolite (i.e. silicalite) membrane has been for the first time demonstrated for selective permeation of hydrated proton (i.e. H3O+) in acidic electrolyte solutions. The silicalite membrane allows for permeation of H3O+ ions, but is inaccessible to the large hydrated multivalent vanadium ions due to steric effect. The silicalite membrane has been further demonstrated as an effective ion separator in the all-vanadium redox flow battery (RFB).The silicalite is nonionic and its proton conductivity relies on the electric field-driven H3O+ transport through the sub nanometer-sized pores under the RFB operation conditions. The silicalite membrane displayed a significantly reduced self-discharge rate because of its high proton-to-vanadium ion transport selectivity. However, the nonionic nature of the silicalite membrane and very small diffusion channel size render low proton conductivity and is therefore inefficient as ion exchange membranes (IEMs) for practical applications. The proton transport efficiency may be improved by reducing the membrane thickness. However, the zeolite thin films are extremely fragile and must be supported on mechanically strong and rigid porous substrates. In this work, silicalite-Nafion composite membranes were synthesized to achieve a colloidal silicalite skin on the Nafion thin film base. The “colloidal zeolite-ionic polymer” layered composite membrane combines the advantages of high proton-selectivity of the zeolite layer and the mechanical flexibility and low proton transport resistance of the ionic polymer membrane. The composite membrane exhibited higher proton/vanadium ion separation selectivity and lower electrical resistance th (open full item for complete abstract)

Committee: Junhang Dong Ph.D. (Committee Chair); Anastasios Angelopoulos Ph.D. (Committee Member); Vikram Kuppa Ph.D. (Committee Member); Joo Youp Lee Ph.D. (Committee Member); Dale Schaefer Ph.D. (Committee Member) Subjects: Chemical Engineering