Investigating Aqueous Zinc Electrolytes for Reversible Metal Electrodeposition Dynamic Windows

Dynamic windows are devices with electronically-controlled transmission, which have gained great attention in recent years due to their ability to decrease the energy demand of a building. These devices improve the energy efficiency of a building by reducing heating and cooling energy costs through the control of light and heat that enters a room. Reversible metal electrodeposition (RME) is a promising approach to the construction of dynamic windows that has been shown to produce fast switching, nontoxic, and color neutral windows. There have been many relatively noble metals such as lead, bismuth, and copper, which have demonstrated different levels of success due their inherent properties. In this respect, zinc has shown to be a surprising viable metal option due to its fast kinetics and reversibility, despite having a large negative reduction potential. By using systematic additions and removal of aqueous supporting ions, we investigated the connection between the zinc window’s electrolyte composition and its optoelectronic performance on transparent indium tin oxide. In doing so, we were able to construct a reversible 25 cm² window with high contrast and >99% Coulombic efficiency. Furthermore, we used scanning electron microscopy to investigate the effect of non-electrochemically active polymers on the zinc window system. We were able to establish a link between the electrodeposited zinc morphology and its effects on device reversibility, Coulombic efficiency, and long-term cycling. This insight allowed us to greatly improve long-term viability of zinc systems through the addition of a polyethylene glycol additive, extending the cycle life from <200 to >1200, while maintaining other beneficiary properties such as a high contrast and reversibility. All considered, these studies highlight important design principles and factors for the construction of zinc RME dynamic windows.