Dynamic Windows Using Reversible Zinc Electrodeposition in Neutral Electrolytes with High Opacity and Excellent Resting Stability

Abstract

electrochemically reduced to the +5 oxidation state. Despite much research studying transition metal oxides and other electrochromic materials including polymers, [18] small molecules, [19] and nanoparticles, [20] there is not yet a single technology that fulfills the color neutrality, switching speed, low cost, and durability required for the widespread adoption of dynamic windows. [21] Compared with electrochromic materials, reversible metal electrodeposition (RME) for dynamic window applications is an underexplored approach that has recently shown great promise. [10,22,23] RME-based devices have several advantages over traditional electrochromic devices. First, metals have high extinction coefficients, which means that uniform metal films are opaque at thicknesses of 20-30 nm. In contrast, electrochromic materials need to be 100-1000 nm thick to block the same amount of light, which can result in slower switching speeds and higher costs. [24][25][26] Second, electrochromic materials are typically deposited using expensive vacuum techniques, while RME devices are mostly solution-processed. [8,26,27] Third, while the most extensively used electrochromic material, WO 3 , is blue in its opaque state, most electrodeposited metal thin films are black, and this color neutrality is desired for the majority of applications. [8,28,29] Dynamic windows harnessing RME are electrochemical devices in which the working electrode is a transparent conductive electrode such as tin-doped indium oxide (ITO) and the counter electrode is a metal frame or mesh. In between the two electrodes, RME devices contain a solution of transparent metal ions in a liquid or gel electrolyte. By applying a negative potential with respect to the working electrode, the metal ions in the electrolyte are reduced to elemental metal on the working electrode, which transforms the device from clear to dark. At the same, metal is oxidized on the counter electrode to form metal ions and charge balance the device. To switch the device from dark to clear, a positive potential is applied to the working electrode to induce the opposite reactions.Most previous RME dynamic windows operate via the electrodeposition of a mixture of Bi and Cu. [8,30,31] Although these devices exhibit fast switching speeds and excellent color neutrality, one disadvantage is the limited solubility of Bi ions in aqueous electrolytes due to the formation of insoluble Bi(OH) 3 . As a result, Bi-Cu electrolytes are typically acidic such that the Bi(OH) 3 is solubilized. The acid in these electrolytes, however, Dynamic windows, which electronically switch between clear and dark states, can play a vital role in energy-efficient buildings by reducing lighting, heating, and cooling demands. In this manuscript, reversible Zn electrodeposition on tin-doped indium oxide electrodes is studied and a mechanism is proposed that explains the deposition and dissolution processes. This mechanistic understanding enables the construction of 100 cm 2 two-electrode devices that transition from clear (80% t...

Reversible Zn2+ Insertion in Tungsten Ion-Activated Titanium Dioxide Nanocrystals for Electrochromic Windows

“…As a result, the pH value of the electrolyte will be stable during the device cycling. This, therefore, will significantly enhance the cycling stability of the devices [30,33]. All these merits enable the ZECDs to become the state-of-the-art focus in the electrochromic community [15,16,20,26,27,29,34].…”

Transparent, High‐Charge Capacity Metal Mesh Electrode for Reversible Metal Electrodeposition Dynamic Windows with Dark‐State Transmission <0.1%

“…Stainless steel (SS) is chemically inert and possesses a high conductivity (1.45 × 10 6 S m −1 and measured sheet resistance of 2.05 Ω □ −1 ), making it an excellent candidate as a counter electrode material, as it has been used in other Zn‐based systems. [ 33,48 ] A CV of the SS mesh in the blank electrolyte shows no Faradaic current in the same potential range, indicating that there are no electrochemical side reactions in the voltage range for RME dynamic windows (Figure 4a, red curve, Table 1). The woven SS mesh was purchased with the same wire diameter as the Cu mesh (30.48 µm), but with a higher pitch (476 µm), which increases the transmission of the mesh by ≈10% (Table 1).…”

High-Vacuum Annealed Al-Doped ZnO Nanorods for Fast-Switching Electrochromic Windows with High-Optical Contrast and Long-Term Stability

“…In recent years, there was a study on Zn-based EC windows utilizing a pH-neutral electrolyte. This enabled them to switch without degradation over 4 weeks as well as have an optical contrast of ∼80% and a switching time of ∼20 s with both transparent and black states . Also, there was research on Cu–Bi-based EC windows introducing a NiO mesh counter electrode.…”