Amorphous bismuth-doped WO3 film: Fast-switching time and high-performance proton-based aqueous electrochromic device

Tungsten trioxide (WO3) film, recognized as one of the most promising electrochromic materials due to its exceptional electrochemical characteristics, is extensively utilized in fabricating electrochromic devices. The use of bismuth-doped WO3 (Bi-WO3) films in photoelectrocatalysis has been extensively studied. However, its potential in electrochromism remains unexplored. Herein, amorphous Bi-WO3 films with enhanced electrochromic performance are synthesized through a simple sol-gel method. The effects of Bi doping amount and sol concentration on the electrochromic properties of Bi-WO3 films are investigated. The optimized Bi-WO3 film displays excellent electrochromic performance, encompassing high optical contrast (Delta T = 81% at 630 nm), fast switching time (2.4/1.2 s for coloring and bleaching), and high coloration efficiency (55.84 cm2C  1). An electrochromic device is assembled utilizing an amorphous Bi-WO3 film as the electrochromic layer with Cu foil as the counter electrode. The fascinating electrochromic properties of amorphous Bi-WO3 thin films and the high activity features of proton enable the assembled ECD to have a suitable working voltage range (1.1 V) in aqueous electrolytes. Besides, the electrochromic device demonstrates outstanding properties (Delta T = 70%, tc = 3 s, tb = 0.9 s) and provides a helpful strategy for the facile processing of high-performance electrochromic devices.