Dynamic windows, which switch between transparent and opaque states upon application of a voltage, have applications in buildings, automobiles, and switchable sunglasses. Here, we describe dynamic windows based on the reversible electrodeposition of Cu and a second metal on transparent indium tin oxide electrodes modified by Pt nanoparticles. Three-electrode cyclic voltammetry experiments reveal that the system possesses high Coulombic efficiency (99.9%), indicating that the metal electrodeposition and stripping processes are reversible. Two-electrode 25-cm 2 windows without bus bars uniformly switch between a transparent state ($80% transmission) and a colorneutral opaque state (<5% transmission) in less than 3 min. These devices switch at least 5,500 times without degradation of optical contrast, switching speed, or uniformity. Taken together, these results indicate that dynamic windows based on reversible metal electrodeposition are a promising alternative to those using traditional electrochromic materials.

Optically tunable windows based on reversible metal electrodeposition are an exciting alternative to static lighting control methods such as blinds and shades. In this Letter, we study reversible Bi/Cu electrodeposition on Pt-modified transparent conducting electrodes for electrochromic applications. Spectroelectrochemical measurements combined with scanning electron microscopy images indicate that the electrolytic Bi:Cu ratio drastically affects the electrode switching speed and electrodeposit morphology, which we propose is due to the galvanic displacement of Bi by Cu+. These findings allow us to construct 25 cm2 black dynamic windows with reversibly tunable transmission at fast switching speeds. This rapid cycling can be maintained over 1000 cycles without degradation in contrast or uniformity. Finally, the Bi–Cu windows consume no power to maintain either their transparency or opacity, making them promising candidates for energy-efficient devices. Their combination of fast switching, color neutrality, durable cycling, and dual-state resting stability make dynamic windows based on Bi–Cu reversible electrodeposition promising and competitive alternatives to traditional electrochromic materials.

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Dynamic windows based on reversible metal electrodeposition are attractive compared to conventional electrochromics because they can have neutral color, high contrast, and potentially lower cost, yet they are not nearly as developed, and the design rules for making them function at large scale are not presented in the literature. We model the voltage drops that occur in the transparent electrodes to get insight on how to obtain uniform electrodeposition of metals over large area. By optimizing the surface and density of the Pt nanoparticles used to nucleate metal growth, we lower the nucleation barrier for electrodeposition by 70 mV. We show that the growth rate of the metal films is determined by diffusion rather than reaction kinetics, which makes it possible to achieve uniform film deposition over a range of potentials from −300 to −700 mV. We demonstrate 100 cm2 dynamic windows that are color-neutral and tint uniformly from a clear state (>60%) to a dark state (<5%) in less than 1 min.