Effect of annealing on acid-treated WO3·H2O nanoplates and their electrochromic properties

• The effect of annealing temperature on acid-treated WO3·H2O nanoplates is reported.
• WO3·H2O nanoplates transformed into WO3 after annealing at 200–400 °C.
• WO3 nanoplates exhibited higher charge density than WO3·H2O nanoplates.
• WO3 nanoplates annealed at 200 °C showed good electrochromic properties.

The effect of annealing temperature on the electrochromic properties of acid-treated hydrated tungsten oxide (WO3·H2O) nanoplates is reported for the first time. Nanoplates were grown on fluorine-doped tin oxide-coated glass substrate using nitric acid, and annealing temperature was varied from 100–400 °C. The as-prepared nanoplates were WO3·H2O, and these nanoplates transformed into tungsten oxide (WO3) after annealing at ≥200 °C. Nanoplate thickness decreased with increasing annealing temperature from 12–55 nm for the as-prepared sample to 12–40 nm for the sample annealed at 400 °C. WO3 nanoplates annealed at 200 °C showed the best electrochromic properties with coloration efficiency of 28.64 cm2 C−1, high optical modulation (58%), good electrochromic cycling stability, as well as short ion insertion and extraction times of ∼9.6 and ∼5.1 s, respectively.