An underlying intercalation ion for fast-switching and stable electrochromism

Electrochromic devices have many important commercial applications ranging from electronic paper like displays, antiglare rear-view mirrors in cars, to energy-saving smart windows in buildings. Monovalent ions such as H⁺, Li⁺, and Na⁺ are widely used as insertion ions in electrochromic devices, but they have limitations such as instability, high cost, and hard handling. The utilization of multivalent ions as insertion ions has been overlooked probably because of the strong electrostatic interactions between ions and intercalation framework as well as the resulted difficulties of intercalation.The bivalent cation, Mg²⁺, has been proved to be efficient electrochromic insertion ions for the electrochromic processes of the nonstoichiometric W₁₈O₄₉ nanowires. Using Mg²⁺ based aqueous electrolyte, the electrochromic W₁₈O₄₉ nanowires shows a short coloration/bleaching time of 2.7/3.6 s, and a high tinting productiveness of 116 cm²/c, together with excellent cyclic constancy. The utilization of bivalent Mg²⁺ as insertion ions will benefit electrochromic devices with low cost, high stability and simple operation.