High-Performance Electrochromic Devices Based on Size-Controlled 2D WO₃ Nanosheets Prepared Using the Intercalation...

It is difficult to obtain ultrathin two-dimensional (2D) tungsten trioxide (WO₃) nanosheets through direct exfoliation from bulk WO₃ in solution due to the strong bonding between interlayers. Herein, WO₃ nanosheets with controllable sizes were synthesized via K⁺ intercalation and the exfoliation of WO₃ powder using sonication and temperature. Because of the intercalation and expansion in the interlayer distance, the intercalated WO₃ could be successfully exfoliated to produce a large quantity of individual 2D WO₃ nanosheets in N-methyl-2-pyrrolidone under sonication. The exfoliated ultrathin WO₃ nanosheets exhibited better electrochromic performance in an electrochromic device than WO₃ powder and exfoliated WO₃ without intercalation. In particular, the prepared small WO₃ nanosheets exhibited excellent electrochromic properties with a large optical modulation of 41.78% at 700 nm and fast switching behavior times of 9.2 s for bleaching and 10.5 s for coloring. Furthermore, after 1000 cycles, the small WO₃ nanosheets still maintained 86% of their initial performance.