Ultra-stable aqueous electrochromism based on [EMIM]⁺/I₃ ^- coordination

Electrochromic (EC) windows are receiving extensive attention owing to their flexibly adjustable optical properties controlled by external bias. Nevertheless, the widespread commercialization of EC windows still faces substantial impediments, including high cost, intricate fabrication processes, slow switching times and especially poor durability. Herein, we propose a facile yet high-performance EC system based on the reversible electrodeposition of iodine, which is theoretically free of "ion-trapping", structure degradation, dendrite growth and corrosion issues encountered by the traditional EC windows. To overcome the polyiodide shuttling problem, the electrolyte is further modified with [EMIM]⁺, which can coordinate with the polyiodide intermediates to form insoluble [EMIM]I₃, and thereby effectively suppress polyiodide formation and shuttling. Moreover, the preferential adsorption of [EMIM]⁺ onto the Zn counter electrode ensures uniform and stable Zn deposition/stripping, synergistically improving the durability of the I₂-Zn EC window. With these multifaceted merits, the simple EC system simultaneously achieves rapid response speeds (t _coloring: 7 s, t _bleaching: 6 s), high optical modulation amplitude (89.6% at 500 nm), impressive coloration efficiency (44.8 cm² C^-1) and excellent lifetime (without performance attenuation after 10 000 cycles). The scaling potential of the system is further demonstrated by constructing a large-area (10 × 10 cm²) device.