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

Tungsten trioxide (WO 3 ) 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 WO 3 (Bi-WO 3 ) films in photoelectrocatalysis has been extensively studied. However, its potential in electrochromism remains unexplored. Herein, amorphous Bi-WO 3 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-WO 3 films are investigated. The optimized Bi-WO 3 film displays excellent electrochromic performance, encompassing high optical contrast (ΔT = 81% at 630 nm), fast switching time (2.4/1.2 s for coloring and bleaching), and high coloration efficiency (55.84 cm 2 C −1 ). An electrochromic device is assembled utilizing an amorphous Bi-WO 3 film as the electrochromic layer with Cu foil as the counter electrode. The fascinating electrochromic properties of amorphous Bi-WO 3 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 (ΔT = 70%, t c  = 3 s, t b  = 0.9 s) and provides a helpful strategy for the facile processing of high-performance electrochromic devices.