Browsing by Subject "Electrochemistry"
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Item Open Access Chemical and Electrochemical Processes at Solid/Liquid Interfaces in Materials for Sanitation and Neural Stimulation(2022) Vasquez Sanchez, Mariana MadelenChemical and electrochemical processes at solid/liquid interfaces are key to diverse and wide range of applications. Hence, the investigation of these reactions is crucial to develop, advance, and improve technologies across numerous fields. The applications chosen as the focus of this dissertation are sanitation and neural stimulation. Sanitation challenges are an urgent global issue for which solutions are being actively developed and improved. This work aims to provide options to overcome some of the limitations found in current technologies in three areas. First, to address user adoption of sanitation facilities, electrochemical modulation of p-cresol was, for the first time, evaluated as an option for malodor nuisance control. It was demonstrated that the electrochemical oxidation of p-cresol can generate 4-hydroxybenzaldehyde following the introduction of chloride ions into the supporting electrolyte. Second, to address nutrient pollution caused by effluents with high levels of ammonium and phosphate from non-sewered sanitation systems and on-site wastewater treatment systems, silicate-based minerals (i.e., clinoptilolite and Polonite) were explored as scalable, affordable, and non-biological options to remove and recover nutrients from these effluents. Clinoptilolite and Polonite were installed and evaluated in our on-site wastewater treatment system, resulting in an increased removal performance of total N and total P from 47.5% to 84.1% and 32.3% to 78.9% respectively. Lastly, to improve the performance of neural stimulation devices, graphenated carbon nanotubes were investigated, for the first time, as an alternative material for neural electrodes. It was demonstrated that graphenated carbon nanotubes can be decorated with platinum nanoparticles to create platinum 3D structures with high cathodal charge storage capacitance and low impedance.
Item Open Access Design, Fabrication and Characterization of Electrochemical Energy Conversion and Storage Devices(2019) Zhou, YihaoThe development of human society strongly relies on the utilization of energy. While fossil fuels are still the main energy source of current human activity, concerns about the environment and the greenhouse effect brought by combustion of fossil fuels have led to tremendous research interest on developing renewable energy conversion and storage techniques. Electrochemical energy technologies represent a promising solution to overcome the current energy dilemma. For energy conversion, photoelectrochemical (PEC) water splitting directly converts water and solar energy into hydrogen and oxygen. The generated hydrogen can be used as a clean, sustainable and efficient fuel and recycled as water after combustion. Currently, photoelectrochemical water splitting devices are either expensive, low performance or unstable. Developing new materials and new architectures with improved PEC performance is in high demand. The first half of this dissertation explores a new earth-abundant chalcogenide material Cu2BaSn(S,Se)4 as a promising photocathode for efficient hydrogen evolution.
For energy storage, supercapacitors are indispensable energy sources for portable electronics and electric vehicles. The rapid development of wearable devices, biomedical implants and electronic skin have raised new mechanical challenges for conventional supercapacitors. Large mechanical deformability is required for supercapacitors to integrate with these stretchable electronics. The second half of the dissertation studied novel stretchable supercapacitors based on various carbon nanomaterials that can be used for the applications of wearable and stretchable electronics.
In chapter 2 and 3, a new solar water splitting photocathode, Cu2BaSn(S,Se)4, was systematically studied. The PEC performance of Cu2BaSn(S,Se)4 was found to increase with increasing Se concentration. However, low light absorption, poor electrolyte/semiconductor junction and poor stability limited the performance of the Cu2BaSn(S,Se)4 photocathode. To improve the photoelectrochemical performance, a Pt/TiO2/CdS/Cu2BaSn(S,Se)4 architecture with ~75% Se concentration was designed. With improved light absorption, enhanced charge separation and charge transfer, a world-record-high photocurrent density of 12.08 mA/cm2 at 0 V/RHE was obtained. The Pt/TiO2/CdS/Cu2BaSn(S,Se)4 photocathode also delivered a consistent photocurrent for more than 10 hours demonstrating superior stability at 0 V/RHE. The same architecture was applied to a solution-processed Cu2BaSn(S,Se)4 absorber and yielded similar PEC performance, demonstrating the feasibility of a high performance, low cost and stable Cu2BaSn(S,Se)4 based photocathode.
From chapter 4 to chapter 7, stretchable supercapacitors based on various carbon nanomaterials were designed, fabricated and characterized. A new stretchable supercapacitor based on crumpled carbon nanotube (CNT) forest was developed. The vertically aligned CNT forest structure was well preserved during the transfer process. Intertwining of neighboring tubes provided the electrical integrity across the whole forest. With large surface area and easily accessible pore structure, a crumpled CNT forest supercapacitor with high electrochemical performance and large mechanical deformability was successfully fabricated. To further reduce the resistance of crumpled CNT forest, an Au-CNT network was introduced at the base. A resistance decrease of an order magnitude was obtained using the Au-CNT network. As a result, the electrochemical performance of the crumpled CNT forest was significantly improved especially at high charge/discharge rate where conductivity is more important.
MXene, a new 2-Dimentional Metal Carbide has also been utilized as a stretchable supercapacitor but was found to crack during the stretchable electrode fabrication process, mainly because of its high mechanical stiffness, weak intersheet interaction and small flake size. Thus, reduced graphene oxide (RGO) was incorporated to overcome these issues. The as-prepared stretchable MXene/RGO composite supercapacitor maintained its structural integrity under various mechanical strains and demonstrated good electrochemical performance.
Finally, inkjet printing was introduced to fabricate a carbon nanotube-reduced graphene oxide-poly(ethylenedioxythiophene) (CNT-RGO-PEDOT) stretchable supercapacitor. The high electrochemical performance (20 F/g, 85% rate capability from 0.5 A/g to 5 A/g) and high mechanical robustness of printed CNT-RGO-PEDOT stretchable supercapacitor demonstrates the possibility of fabricating stretchable supercapacitor in a more scalable approach.
Item Open Access Electrochemical Disinfection of Liquid Human Waste Using Potentiodynamic Methods and Controlled Electrode Surface Chemistry(2018) Thostenson, James OwenRoughly 40% of the world does not have access to appropriate sanitation of human generated waste water. Lack of infrastructure and poverty in developing nations has stymied the deployment of conventional sewage treatment practices. In helping to solve this global issue requires the development of an energy efficient, cost-effective, low-maintenance, and decentralized toilet system that can remediate human liquid waste, or, blackwater. Herein, electrochemical disinfection as a means of treating blackwater is investigated using degenerately boron-doped diamond and Magnéli-phase titanium sub-oxide electrodes. It is found that both can be operated in potentiodynamic modes to control surface chemistry and improve generation of biocidal oxidants such as hydrogen peroxide and chlorine
in blackwater containing solutions. Use of a packed-bed electrochemical reactor is also studied in the treatment of blackwater using Magnéli-phase titanium sub-oxide granular electrodes. It is found that bed-height, flow-rate, and blackwater chemistry
can greatly affect the effectiveness of electrochemical disinfection and stability of a packed-bed electrochemical reactor. Overall, these results highlight how existing electrode materials can be modified or controlled in-situ to inhibit fouling, generate
oxidants using less energy, and therefore disinfect blackwater pathogens more effectively.
Item Open Access Methoxy-derivatization of alkyl chains increases the in vivo efficacy of cationic Mn porphyrins. Synthesis, characterization, SOD-like activity, and SOD-deficient E. coli study of meta Mn(III) N-methoxyalkylpyridylporphyrins.(Dalton transactions (Cambridge, England : 2003), 2011-04) Tovmasyan, Artak G; Rajic, Zrinka; Spasojevic, Ivan; Reboucas, Julio S; Chen, Xin; Salvemini, Daniela; Sheng, Huaxin; Warner, David S; Benov, Ludmil; Batinic-Haberle, InesCationic Mn(III) N-alkylpyridylporphyrins (MnPs) are potent SOD mimics and peroxynitrite scavengers and diminish oxidative stress in a variety of animal models of central nervous system (CNS) injuries, cancer, radiation, diabetes, etc. Recently, properties other than antioxidant potency, such as lipophilicity, size, shape, and bulkiness, which influence the bioavailability and the toxicity of MnPs, have been addressed as they affect their in vivo efficacy and therapeutic utility. Porphyrin bearing longer alkyl substituents at pyridyl ring, MnTnHex-2-PyP(5+), is more lipophilic, thus more efficacious in vivo, particularly in CNS injuries, than the shorter alkyl-chained analog, MnTE-2-PyP(5+). Its enhanced lipophilicity allows it to accumulate in mitochondria (relative to cytosol) and to cross the blood-brain barrier to a much higher extent than MnTE-2-PyP(5+). Mn(III) N-alkylpyridylporphyrins of longer alkyl chains, however, bear micellar character, and when used at higher levels, become toxic. Recently we showed that meta isomers are ∼10-fold more lipophilic than ortho species, which enhances their cellular accumulation, and thus reportedly compensates for their somewhat inferior SOD-like activity. Herein, we modified the alkyl chains of the lipophilic meta compound, MnTnHex-3-PyP(5+) via introduction of a methoxy group, to diminish its toxicity (and/or enhance its efficacy), while maintaining high SOD-like activity and lipophilicity. We compared the lipophilic Mn(III) meso-tetrakis(N-(6'-methoxyhexyl)pyridinium-3-yl)porphyrin, MnTMOHex-3-PyP(5+), to a hydrophilic Mn(III) meso-tetrakis(N-(2'-methoxyethyl)pyridinium-3-yl)porphyrin, MnTMOE-3-PyP(5+). The compounds were characterized by uv-vis spectroscopy, mass spectrometry, elemental analysis, electrochemistry, and ability to dismute O(2)˙(-). Also, the lipophilicity was characterized by thin-layer chromatographic retention factor, R(f). The SOD-like activities and metal-centered reduction potentials for the Mn(III)P/Mn(II)P redox couple were similar-to-identical to those of N-alkylpyridyl analogs: log k(cat) = 6.78, and E(1/2) = +68 mV vs. NHE (MnTMOHex-3-PyP(5+)), and log k(cat) = 6.72, and E(1/2) = +64 mV vs. NHE (MnTMOE-3-PyP(5+)). The compounds were tested in a superoxide-specific in vivo model: aerobic growth of SOD-deficient E. coli, JI132. Both MnTMOHex-3-PyP(5+) and MnTMOE-3-PyP(5+) were more efficacious than their alkyl analogs. MnTMOE-3-PyP(5+) is further significantly more efficacious than the most explored compound in vivo, MnTE-2-PyP(5+). Such a beneficial effect of MnTMOE-3-PyP(5+) on diminished toxicity, improved efficacy and transport across the cell wall may originate from the favorable interplay of the size, length of pyridyl substituents, rotational flexibility (the ortho isomer, MnTE-2-PyP(5+), is more rigid, while MnTMOE-3-PyP(5+) is a more flexible meta isomer), bulkiness and presence of oxygen.Item Open Access Modified INOvent for delivery of inhaled nitric oxide during cardiac MRI.(Magn Reson Imaging, 2011-10) Devendra, Ganesh P; Hart, Stephen A; Kim, Yuli Y; Setser, Randy M; Flamm, Scott D; Krasuski, Richard ABACKGROUND: The aim of this study was to assess the feasibility of delivering NO through a modified system to allow clearance of the magnetic field and thus compatibility with cardiac magnetic resonance (CMR). Nitric oxide (NO) is an inhalational, selective pulmonary vasodilator with a wide range of applications in a variety of disease states, including diseases that affect the right ventricle. Accurate assessment of dynamic changes in right ventricular function necessitates CMR; however, delivery of NO is only possible using equipment that is not magnetic resonance imaging (MRI) compatible (INOvent delivery system, Ohmeda, Inc., Madison, WI, USA). METHODS: The INOvent delivery system was modified by using 35 ft. of standard oxygen tubing to allow NO delivery through an electrical conduit and into the MRI suite. The concentrations of oxygen (O(2)), nitrogen dioxide (a harmful byproduct, NO(2)) and NO were measured in triplicate using the built-in electrochemical analyzer on the INOvent. After confirmation of safety, the system was used to administer drug to a patient x, and dynamic MRI measurements were performed. RESULTS: When the standard INOvent was set to administer 40 ppm of NO, the mean/standard deviation of gas delivered was as follows: NO: 42/0 ppm; NO(2): 0.3/0.1 ppm; and O(2): 93/0 ppm. In comparison, the gas delivery of the modified INOvent was follows: NO: 41/0 ppm; NO(2): 0.5/0 ppm; and O(2): 93.7/0.6 ppm. During administration to an index patient with severe pulmonic insufficiency (PI), a measurable reduction in PI was observed by CMR. CONCLUSIONS: Nitric oxide can be administered through 35 ft. of standard oxygen tubing without significantly affecting dose delivery. This technique has potential application in patients with right-sided structural heart disease for determination of dynamic physiological changes.Item Open Access Nitrogen-Oxidants Enable Group-Transfer Reactions(2021) Ayer, Suraj KumarSynthetic technologies can enable transformation of polarizable carbon–carbon (C=C) bonds and typically inert carbon–hydrogen (C–H) bonds into value-added diverse functional groups. Such technologies streamline access to complex molecules. In recent years, nitrogen-centered oxidants have garnered significant attention as a result of their ability to engage in selective and predictable synthetic transformations of these groups. Within this broad class of reactions, herein disclosed are investigations into two complementary approaches to access and utilize nitrogen-centered oxidants. Of these, the first approach advances iron nitrenoids to affect substrate-limited aziridination reactions of carbon–carbon double bonds. Specifically, Chapter two documents a best-in-class method that relies on limiting quantities of electronically varied styrene substrates to furnish synthetically useful aziridines in moderate to good yields under mild conditions. Subsequently, an orthogonal approach is developed – one that demonstrates the viability sulfamate esters as precursors to radical intermediates that template C–H functionalization reactions, with a focus on two group-transfer processes. Through this research, sulfamate esters have been identified as precursors to a modern class of nitrogen-centered oxidants, sulfamyl radicals. To enable broader usage, Chapter three discloses a new general and mild method to access substrates for this approach, employing inexpensive readily available sulfur trioxide sources with a wide range of ubiquitous amine and alcohol starting materials. The method relies on activation of a common intermediate, a sulfamic acid salt, to generate a large variety of N, O-disubstituted sulfamate esters and sulfamides. Studies described in Chapters four and five have resulted in mild strategies to generate sulfamyl radicals from sulfamate esters. These sulfamyl radicals engage in a rare, 1,6-hydrogen-atom transfer processes to affect position-selective C(3)-functionalization of aliphatic C–H bonds. More specifically, in Chapter four, this rare property is harnessed to establish a C(3)-selective xanthylation process. Enabled by visible-light, xanthylation of primary, secondary, and tertiary centers has been demonstrated with exquisite site selectivity. This investigation confirms the scientific insight that N-functionalized sulfamate esters enable complementary site selectivity to the previously known methods employing nitrogen-centered radicals. Additionally, this C(3)-xanthylation reaction can be combined with known technologies to affect formal C(sp3)–H azidation, thiolation, trifluoromethylthiolation, deuteration, allylation, and vinylation to generate molecular diversity from a common intermediate. Building on this foundation, Chapter five documents a photoredox-mediated method to generate the requisite sulfamyl radicals for site-selective carbon-carbon and carbon-oxygen bond forming processes. These investigations are the first of their kind to generate sulfamyl radicals from non-pre-oxidized sulfamate esters. These nitrogen-centered sulfamyl radicals, through the sulfamate-templated 1,6-HAT process, furnish secondary and tertiary carbon-centered radicals which can be trapped by Michael acceptors for a formal C(3)-alkylation. This process yields products with diastereoselectivity when engaging complex small molecules and enantioenriched Michael acceptors. Thereby, photoredox-mediated C(3)-selective alkylation process affords complementary position selectivity to that was achieved using known photoredox–mediated carbon-carbon bond-forming reactions. Finally, Chapter six describes electrochemical methods to generate the key sulfamyl radicals. Through this research, the first example of direct anodic oxidation of sulfamate ester anions is disclosed. The resultant sulfamyl radicals are utilized to affect novel C(3)-hydroxylation reactions. The electrochemical method is further extended to affect N-alkylation of sulfamate esters and sulfamides. Together, conceptual innovations have facilitated mild methods to access the nitrogen-centered oxidants for the functionalization of carbon–carbon (C=C) bond and radical-mediated functionalization of remote C(3)-aliphatic C–H bonds. These investigations enable synthetic disconnections that would be infeasible using previously established methods and provide efficient access to new chemical space.
Item Open Access The Roles of Capping Agents and Defects in the Anisotropic Growth of Ag Nanocrystals(2023) Xu, HengSynthetic control of metal nanocrystal shape is a common strategy to control their properties. Shape control is often achieved by controlling the crystal structure of the seed crystals, as well as through the use of additives which are thought to block atomic addition to certain facets. However, the effect of crystal structure or additives on the rate of atomic addition to a specific facet is not usually quantified, making it difficult to design nanocrystal syntheses. This work combines seed-mediated growth, single-crystal electrochemistry measurements and Raman spectroscopy to understand the roles of capping agents and planar defects in the anisotropic growth of silver nanocrystals. The roles of citrate, polyvinylpyrrolidone (PVP), and halides have been investigated. Synthetic results show citrate is a {111} capping agent, PVP is a weak {111} capping agent, chloride and bromide are weak {100} capping agents. However, when chloride or bromide is added with PVP, they become strong {100} capping agents. Electrochemical measurements show the anisotropic growth is caused by capping agents selectively suppressing the oxidation of ascorbic acid (a reducing agent) on a specific crystal facet. The effect of capping agents on silver ion reduction is not facet-selective. Further comparison between the growth of single-crystal seeds and seeds with planar defects indicates defects can catalyze silver atom deposition by up to 100 times and cause greater anisotropic growth than can be explained by facet-selective passivation. Overall this work advances our understanding of nanocrystal chemistry, and informs the design of nanocrystal synthesis to obtain a desired nanocrystal morphology with a desired set of properties.