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

It is difficult to obtain ultrathin two-dimensional (2D) tungsten trioxide (WO) nanosheets through direct exfoliation from bulk WO in solution due to the strong bonding between interlayers. Herein, WO nanosheets with controllable sizes were synthesized via K intercalation and the exfoliation of WO powder using sonication and temperature. Because of the intercalation and expansion in the interlayer distance, the intercalated WO could be successfully exfoliated to produce a large quantity of individual 2D WO nanosheets in -methyl-2-pyrrolidone under sonication. The exfoliated ultrathin WO nanosheets exhibited better electrochromic performance in an electrochromic device than WO powder and exfoliated WO without intercalation. In particular, the prepared small WO 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 WO nanosheets still maintained 86% of their initial performance.