Electrochemical Characterization of Organic Polymers And Their Applications for Renewable Energy

Renewable energy technologies are clean resources of energy that have a much lower environmental impact than conventional energy technologies such as coal or petroleum. Renewable energy technologies can help to reduce energy imports and the use of fossil fuel which is the largest source of U.S. carbon dioxide emissions. Organic polymers have received significant interest as key materials for renewable energy. Conducting polymers with tunable electrical conductivities could serve as electrodes or active materials for various electronic devices. Semiconducting polymers with tunable band gaps are great candidates as the semiconducting layers of optoelectronic devices such as organic solar cells. Also, both conducting polymers and insulating polymers have been explored for energy storage devices such as active materials, separators, electrolytes, pseudocapacitors, and so on. In addition, conventional plastics are the most widely used materials due to their durability, longevity, impermeability, good strength to mass ratio compared to metals, wood, and glass. This thesis is situated at the intersection of analytical and electrochemistry of various ranges of polymers and their engineering application for sustainability. Although the organic solar cell is a promising technology, it has a relatively short lifetime due to poor long-term stability, making it a challenge for commercialization. In chapter 2, we investigated a random sequence copolymer containing a conjugated poly(3-hexylthiophene) backbone and fullerene-functionalized side chains that serve as a general blend stabilizer for an organic solar cell device. We found that this copolymer could stabilize morphology for multiple blends in thin films and the active layer of organic solar cell devices and enhance the thermal stability of the devices. Understanding and developing of copolymer compatibilizer should play an important role to improve device performance and stability. A redox flow battery is a rising area in the secondary battery due to its advantages such as design flexibility, safety, and scalability. In chapter 3, we discussed the modified design of a nonaqueous redox flow battery containing a high effective concentration of redox-active materials in insoluble polymer beads. A bulk of charge can be stored on redox-active moieties covalently tethered to non-circulating, insoluble polymer beads. The charge is rapidly transferred between the electrodes and the beads through soluble redox-matched mediators. With the functionalized beads, the battery capacity increased without the need to make high solubility redox-active molecules. In chapter 4, we develop an electrosynthetic approach to repurpose poly(vinyl chloride), which has a low recycling rate in most countries. The chlorine atoms from PVC are recovered under electroreductive conditions and then directly repurposed as a feedstock in a tandem electrooxidative chlorination reaction. Also, we discovered a redox mediator that facilitates the reductive dechlorination reaction. The proposed mechanism of the reduction process was informed by cyclic voltammetry and bulk electrolysis analyses. This approach has good potential that PVC waste that we made in our life as a chlorine source can be repurposed to produce value-added products.PhDMacromolecular Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/172562/1/dukhan_1.pd

Thermal assessment of forced convection through metal foam heat exchangers

Using a thermal resistance approach, forced convection heat transfer through metal foam heat exchangers is studied theoretically. The complex microstructure of metal foams is modeled as a matrix of interconnected solid ligaments forming simple cubic arrays of cylinders. The geometrical parameters are evaluated from existing correlations in the literature with the exception of ligament diameter which is calculated from a compact relationship offered in the present study. The proposed, simple but accurate, thermal resistance model considers: the conduction inside the solid ligaments, the interfacial convection heat transfer, and convection heat transfer to (or from) the solid bounding walls. The present model makes it possible to conduct a parametric study. Based on the generated results, it is observed that the heat transfer rate from the heated plate has a direct relationship with the foam pore per inch (PPI) and solidity. Furthermore, it is noted that increasing the height of the metal foam layer augments the overall heat transfer rate; however, the increment is not linear. Results obtained from the proposed model were successfully compared with experimental data found in the literature for rectangular and tubular metal foam heat exchangers

A Nonaqueous Redox-Matched Flow Battery with Charge Storage in Insoluble Polymer Beads

We describe the nonaqueous redox-matched flow battery (RMFB), where charge is stored on redox-active moieties covalently tethered to non-circulating, insoluble polymer beads and charge is transferred between the electrodes and the beads via soluble mediators with redox potentials matched to the active moieties on the beads. The RMFB reported herein uses ferrocene and viologen derivatives bound to crosslinked polystyrene beads. Charge storage in the beads leads to a high (approximately 1.0-1.7 M) effective concentration of active material in the reservoirs while preventing crossover of that material. The relatively low concentration of soluble mediators (15 mM) eliminates the need for high-solubility molecules to create high energy density batteries. Nernstian redox exchange between the beads and redox-matched mediators was fast relative to the cycle time of the RMFB. This approach is generalizable to many different redox-active moieties via attachment to the versatile Merrifield resin

Size Control in the Synthesis of 1–6 nm Gold Nanoparticles via Solvent-Controlled Nucleation

We report a facile synthetic route for size-controlled preparation of gold nanoparticles. Nearly monodisperse gold nanoparticles with core diameters of 1–6 nm were obtained by reducing AuP(Phenyl)₃Cl with <i>tert</i>-butylamine borane in the presence of dodecanethiol in the solvent mixture of benzene and CHCl₃. Mechanism studies have shown that the size control is achieved by the solvent-controlled nucleation in which the nuclei concentration increases with increasing the fraction of CHCl₃, leading to smaller particles. It was also found that, following the solvent-controlled nucleation, particle growth occurs via ligand replacement of PPh₃ on the nuclei by Au(I)thiolate generated by the digestive etching of small particles. This synthetic strategy was successfully demonstrated with other alkanethiols of different chain length with which size-controlled, monodisperse gold nanoparticles were prepared in remarkable yield without requiring any postsynthesis treatments

A Nonaqueous Redox-Matched Flow Battery with Charge Storage in Insoluble Polymer Beads**

We describe the nonaqueous redox-matched flow battery (RMFB), where charge is stored on redox-active moieties covalently tethered to non-circulating, insoluble polymer beads and charge is transferred between the electrodes and the beads via soluble mediators with redox potentials matched to the active moieties on the beads. The RMFB reported herein uses ferrocene and viologen derivatives bound to crosslinked polystyrene beads. Charge storage in the beads leads to a high (approximately 1.0–1.7 M) effective concentration of active material in the reservoirs while preventing crossover of that material. The relatively low concentration of soluble mediators (15 mM) eliminates the need for high-solubility molecules to create high energy density batteries. Nernstian redox exchange between the beads and redox-matched mediators was fast relative to the cycle time of the RMFB. This approach is generalizable to many different redox-active moieties via attachment to the versatile Merrifield resin.A new redox-flow battery architecture, the redox-matched flow battery, wherein charge is stored on redox-active moieties covalently tethered to non-circulating, insoluble polymer beads and charge is transferred between the electrodes and the beads via soluble mediators with redox potentials matched to the active moieties on the beads. This enables high energy densities without crossover of bead-bound active material.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/172262/1/chem202200149-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172262/2/chem202200149_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172262/3/chem202200149.pd

Substrate and buffer layer effect on the structural and optical properties of graphene oxide thin films

Graphene oxide (GO) thin films on various substrates show surprising variations of their structural and optical properties. These variations were also studied by depositing GO via introducing a gold nanoparticles buffer layer on quartz substrate. The effect of the substrate as well as buffer layer results in short range order crystallization in deposited GO films with an increase in inter-planar spacing. XPS analysis shows that GO undergoes reduction when spin coated on ITO/glass substrate. The deposited GO films exhibit luminescence emission, and the introduction of gold buffer layer results in a blue shift of the photoluminescent emission spectra. The GO on gold buffer layer shows almost constant optical absorption in the whole visible spectral region like graphene. The present study indicates that buffer layer effects and the interaction between different substrates and GO is strong enough to affect the oxygen linkages in GO which in turn changes its structural and optical properties, which may find potential application in graphene based optoelectronic device fabrication.close5

Impact of particulate deposition on the thermohydraulic performance of metal foam heat exchangers: a simplified theoretical model

Assuming uniform particulate deposit layer, with deposition layer thickness in the range of 10-400 μm, on the ligaments of a metal foam heat sink, the effects of airborne particle deposition on the steady-state thermohydraulic performance of a metal foam heat sink are examined theoretically. Using a cubic cell model, changes in the foam internal structure, due to deposition, have been theoretically related to the increased pressure drop due to partial blockage of the pores. Our results suggest that the fouled to clean pressure drop ratio is only a function of the ligament to pore diameter ratio. Another interesting observation is that, compared to clean foams, the pressure drop can increase by orders of magnitude depending on the extent to which the pores are blocked. To examine the fouling effects on heat transfer from the foams, a thermal resistance network has been used. Moreover, the heat transfer from metal foams is more affected by fouling at higher fluid velocities. For example, when air is pushed through foams which their ligaments are uniformly covered by particles at 3 m/s, up to 15 decrease in the total heat transfer from the heated surface is predicted