High-Performance Electrochromic Devices Based on Size-Controlled 2D WO 3 Nanosheets Prepared Using the Intercalation Method.

It is difficult to obtain ultrathin two-dimensional (2D) tungsten trioxide (WO 3 ) nanosheets through direct exfoliation from bulk WO 3 in solution due to the strong bonding between interlayers. Herein, WO 3 nanosheets with controllable sizes were synthesized via K + intercalation and the exfoliation of WO 3 powder using sonication and temperature. Because of the intercalation and expansion in the interlayer distance, the intercalated WO 3 could be successfully exfoliated to produce a large quantity of individual 2D WO 3 nanosheets in N -methyl-2-pyrrolidone under sonication. The exfoliated ultrathin WO 3 nanosheets exhibited better electrochromic performance in an electrochromic device than WO 3 powder and exfoliated WO 3 without intercalation. In particular, the prepared small WO 3 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 3 nanosheets still maintained 86% of their initial performance.