Christopher Barile1,Desmond Madu1,Nikhil Bhoumik1,Cheon Woo Moon1
University of Nevada, Reno1
Christopher Barile1,Desmond Madu1,Nikhil Bhoumik1,Cheon Woo Moon1
University of Nevada, Reno1
Dynamic windows harnessing reversible metal electrodeposition (RME) have emerged as a promising technology to enable energy-efficient windows with electronically tunable transmission. Metals are ideal materials for blocking light due to their high opacity and color neutrality. Most previous work on metal-based dynamic windows using aqueous electrolytes relies on the reversible electrodeposition of Ag, Cu, and Bi.<sup>1-3</sup> These metals are more noble than H<sub>2</sub>, and thus H<sub>2</sub> evolution can be avoided during device switching.<br/><br/>Recently, we were inspired by work on secondary Zn batteries<sup>4</sup> to develop aqueous Zn electrolytes for reversible metal electrodeposition for dynamic windows. Despite being substantially less noble than H<sub>2</sub> with a standard reduction potential of -0.76 V vs. SHE, reversible Zn electrodeposition can be conducted with high Coulombic efficiency with properly designed electrolytes. We find that H<sub>2</sub> evolution can be kinetically passivated by Zn, ZnO, and Zn(OH)<sub>2</sub> electrodeposits. Moreover, because the solubility of common Zn salts in water is much higher than those of Ag, Cu, and Bi, high concentration electrolytes can be designed that results in rapid metal electrodeposition. Zn also can be electrodeposited with a much more compact morphology than other explored metals, which allows for Zn-based dynamic windows to reach privacy-level transmission in less than one minute. We also demonstrate that Zn-based dynamic windows can cycle 10,000 times without significant degradation, and they exhibit excellent bistability. Taken together, these results highlight that Zn is a promising candidate for practical metal-based dynamic windows.<br/><br/>1. Barile, C. J.; Slotcavage, D. J.; Hou, J.; Strand, M. T.; Hernandez, T. S.; McGehee, M. D. “Dynamic Windows with Neutral Color, High Contrast, and Excellent Durability using Reversible Metal Electrodeposition,” <i>Joule</i>, <b>2017</b>, <i>1</i>, 133-145.<br/>2. Ziegler, J. P.; Howard, B. M. “Applications of Reversible Electrodeposition Electrochromic Devices,” <i>Sol. Energy Mater. Sol. Cells</i>, <b>1995</b>, <i>39</i>, 317-331.<br/>3. de Mello, D. A. A.; Oliveira, M. R. S.; de Oliveira, L. C. S.; de Oliveira, S. C. “Solid Electrolytes for Electrochromic Devices based on Reversible Metal Electrodeposition,” <i>Sol. Energy Mater. Sol. Cells</i>, <b>2012</b>, <i>103</i>, 17-24.<br/>4. Wang, N.; Wan, H.; Duan, J.; Wang, X.; Tao, L.; Zhang, J.; Wang, H. “A Review of Zinc-based Battery from Alkaline to Acid,” <i>Mater. Today Adv.</i>, <b>2021</b>, <i>11</i>, 100149-100167.