Electrochromism Enabled by Br<sup>-</sup>/Br<sub>3</sub><sup>-</sup> Conversion.

Wan, Jiangbei; Chen, Yingyu; Li, Zhaotao; Fan, Bowen; Guo, Xianglin; Cong, Shan; Wang, Zhen; Zhao, Zhigang · Nano Lett · 2025

basic_science · Level V

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Abstract

Redox reactions in halogen ion systems, characterized by fast kinetics and significant reversibility, have broad applications in energy storage, catalysis, electrodialysis, and other fields. However, due to the opacity of the system and product stability, the redox halogen systems have not yet been applied to reversible optical modulation. In this study, efficient and reversible Br<sup>-</sup>/Br<sub>3</sub><sup>-</sup> conversion is achieved with the assistance of CNTs and 1-methyl-3-propylimidazolium ions (MPI<sup>+</sup>), which catalyze the oxidation of Br<sup>-</sup> on the current collector. Based on the Br<sup>-</sup>/Br<sub>3</sub><sup>-</sup> redox reaction, the constructed electrochromic device (ECD) achieves optical modulation from colorless to bright yellow, exhibiting an impressive optical modulation of 64.0% and excellent cycling stability with 97.0% optical modulation retained after 3000 cycles. This device features a simplified structure and ease of fabrication, offering a promising approach for the future development of diverse electrochromic technologies.