Investigation of an Electrochromic Device Based on Ammonium Metatungstate-Iron (II) Chloride Electrochromic Liquid

Even though electrochromism has been around for more than 50 years, it still has several issues. Multi-layered films, high manufacturing costs, and a short lifetime are present in existing electrochromic devices. We demonstrate a unique high-performance device with a basic structure and no solid electrochromic sheets in this work. In this device, the electrolyte layer is also avoided. The device uses an electrochromic solution prepared from a mixture of ammonium metatungstate and iron (II) chloride solution as a functional layer with reversible redox properties. The tungstate ions on the electrode surface are reduced when the device is colored, and the Fe2+ on the electrode surface is oxidized on another electrode surface. The generated Fe3+ in the mixed functional layer oxidizes the previously reduced tungstate ions as the device fades. We determined the Delta T (transmittance modulation) and response time among ammonium metatungstate ratios, iron (II) chloride ratios, and driven current density using DOE (design of experiment) trials. Using 0.175 mol/L ammonium metatungstate and 0.30 mol/L iron (II) chloride, a device with outstanding Delta T (more than 57% at 700 nm), a short response time (less than 10 s), and high coloring efficiency (160.04 cm(2)/C at 700 nm) is demonstrated.

Automated summary

This study demonstrates a high-performance electrochromic device with a basic structure that does not use solid electrochromic sheets and avoids the electrolyte layer. By using an electrochromic solution prepared from a mixture of ammonium metatungstate and iron (II) chloride, outstanding transmittance modulation, short response time, and high coloring efficiency were achieved.