Pulsed Electrodeposition for Dynamic Windows Based on Reversible Metal Electrodeposition

Dynamic windows enable electronic control of light and heat flow into and out of buildings, improving energy efficiency and building aesthetics to boost user experience. Dynamic windows based on reversible metal electrodeposition (RME) operate by the reversible electroplating of metal ions (e.g. Cu and Bi) onto a transparent conducting oxide (TCO) to block light. This process occurs when a reductive potential sufficient for metal plating is applied. However, when using direct current (DC) at a fixed reductive potential for electrodeposition, the metal film suffers from a rough and dendritic morphology, limiting its ability to block light and the tinting speed to a desired opacity.

Here, we report a method that enables electrodeposition of smooth and dense metal films and thus faster tinting speed. Instead of DC electrodeposition, we use pulsed electrodeposition with a 10% duty cycle and a 1 Hz frequency during tinting. This technique allows restoration of the concentration profile near the electrodeposition surface during the off pulse, preventing undesirable dendritic growth of metals. While these films tint slower initially compared to DC electrodeposition, the films using this pulsing protocol reach 0.1% transmittance faster (45% reduction) due to a uniform and smooth film morphology that blocks light more efficiently. We realize the benefits of both protocols by implementing a DC step of 10 s before switching to pulsing resulting in a 58% reduction in tinting time to 0.1% transmittance. Finally, we advanced the durability of RME dynamic windows by employing a pulsed voltage cycling profile when stripping the metal from the TCO working electrode and plating it on the metal mesh counter electrode. The pulsing dramatically reduced dendrite growth on the mesh, allowing the windows to maintain consistent optical contrast and coloration efficiency after 2,400 cycles to 10% transmittance. These windows have better color neutrality than conventional WO₃ electrochromic windows and also have the ability to block 99.9% of the visible light, which is essential for applications where privacy is desired.