Abstract: Aqueous zinc-ion electrochromic devices (Zn-ions Electrochromic devices, ZECDs) combine the high safety and high ionic conductivity of aqueous electrolytes, and they have broad application prospects in smart windows and smart displays. At this stage, researchers mainly use a single zinc salt aqueous solution as the electrolyte to build ZECDs. But zinc metal electrodes in a single zinc salt aqueous electrolyte easily undergo side reactions like hydrogen evolution and dendrite growth, which leads to poor cycling stability of the device. For this, this study developed a Zn²⁺/NH₄⁺ mixed electrolyte system and successfully designed and built ZECDs with a Nb₁₈W₁₆O₉₃/mixed electrolyte/Zn structure. We studied the device’s electrochemical and electrochromic performance using methods like electrochemical-spectroscopic in situ testing. Test analysis results show that Nb₁₈W₁₆O₉₃ films have excellent long-term cycling stability in three electrolytes using a three-electrode system and good structural stability. Compared to a single electrolyte system, devices show better electrochromic performance in a Zn²⁺/NH₄⁺ mixed electrolyte system. The optical modulation at 630 nm can reach up to 68%. After 1200 cycles, the device still retains 82.3% of its initial capacity, with the light modulation still holding at 69.7% of its original value. In the mixed system, Zn²⁺ achieves high light modulation due to its high charge density, while NH₄⁺ optimizes the solvation structure through its unique hydrogen bond network. The synergy between Zn²⁺ and NH₄⁺ not only stabilizes the electrode structure but also suppresses dendrite growth on the zinc electrode, effectively improving the device's electrochromic and electrochemical performance. This study confirms that the Zn²⁺/NH₄⁺ mixed electrolyte system can effectively enhance the electrochemical activity and cycling stability of ZECDs, providing experimental support and research ideas for designing and optimizing high-performance aqueous zinc-based electrochromic devices.

Key words: electrochromic device, Nb₁₈W₁₆O₉₃, mix electrolyte