Electrochemical Characterization of Organic Polymers And Their Applications for Renewable Energy

Abstract

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.