A high-performance multifunctional three-electrode electrochromic device based on a Zn auxiliary electrode

Electrochromic materials exhibit electrically tunable optical properties and are widely applied in smart windows, optical switches, and photonic devices. However, the modulation amplitude of conventional electrochromic devices (ECDs) is fundamentally constrained by sluggish ion diffusion and incomplete redox reactions. Herein, we report a high-performance three-electrode electrochromic device (TRECD) incorporating a zinc (Zn) auxiliary electrode. The Zn auxiliary electrode can introduce additional Zn²⁺ into the device and participate in the electrochemical reaction, effectively enhancing the device performance. By optimizing the Li⁺/Zn²⁺ ratio in the electrolyte, the TRECD achieves substantially enhanced electrochemical and optical performance, including an 18-fold increase in areal capacitance, ultrafast response times (1.43 s for coloring and 2.72 s for bleaching), a record-high coloration efficiency of 603.37 cm² C⁻¹, and an exceptional optical modulation amplitude of 98.1%, reaching a minimum transmittance of 0.2%. This unprecedented contrast enables reversible switching between nearly full transparency and near-zero transmittance. Our results demonstrate that introducing an auxiliary Zn electrode and leveraging its coupled ion chemistry offers a powerful strategy for boosting the efficiency and functionality of electrochromic systems. This three-electrode structure opens new pathways for high-contrast optical switches, tunable filters, smart windows, and reconfigurable photonic devices.