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Investigating Reversible Zinc Electrodeposition Dynamic Windows
AdvisorBarile, Christopher J
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The current energy crisis is a growing and unrelenting problem that affects all of humanity. A problem that only seems to grow with the increasing world population leading to greater and greater energy demand from unrenewable and environmentally harmful sources. As such, energy sustainability is an expanding field attracting great interest. Dynamic windows have emerged as a potential solution in recent years as a technology that allows for a large decrease in energy consumption. Dynamic windows allow for controllable transparency through the application of a voltage, which in turn allows for greater control of the amount of light and heat in a building. This control leads to a reduction in the heating and cooling needed in a building to provide a comfortable environment and thus energy savings. However, current methods of creating dynamic windows have encountered hurdles that prevent the technology from being adopted widely. Dynamic windows that employ reversible metal electrodeposition (RME) allow for the construction of devices with high contrast, multiple optical states between 80% and <1% transmission, and high reversibility for a long cycle life. RME possesses several advantages over other forms of dynamic window, however, many of these benefits depend on the metal used in the electrolyte of the RME window. Electrolytes that enable the coelectrodeposition of Bi and Cu are leading candidates for use in RME windows due to their ability to support high contrast, fast, color-neutral, and reversible windows. In this dissertation, I detail progress made to address the low pH environment necessitated by the low solubility of Bi in water under neutral or alkaline conditions. I use chelating agents to bind to Bi, which allow for greater solubility at higher pH. This change leads to less etching of the transparent conducting working electrode and extends shelf life and viability of the Bi-Cu window. Zn electrolytes are another promising metal candidate for use in RME dynamic window electrolytes. The majority of this dissertation focuses on the use of Zn to create highly reversible electrolytes, some with Coulombic efficiencies as high as 99%. I examine the effect that anions such as halides and sulfate have on the spectroelectrochemical performance of different electrolytes. I further build a connection between the morphology of the Zn electrodeposits and window performance. I utilize techniques such as X-ray diffraction and scanning electron microscopy to study the Zn surface layer after electrodeposition, I analyze how dendritic and uneven morphology hinder long term cyclability. Using this knowledge, I employed methods such as the use of polymers in the electrode to create a three-electrode device that can cycle over 1,000 times as well as a practical two-electrode device that cycles over 100 times. I also designed a novel method of construction of dynamic windows through the employment of water-in-salt electrolytes (WISe). As opposed to traditional salt-in-water electrolytes, WISe facilitated Zn electrodeposition that does not generate side products such as ZnO or Zn(OH)2. This discovery as well as others written about in this dissertation illustrate the viability and promise of Zn for RME dynamic windows and serves as the basis for further modification and improvements.