Effect of pH on the structure and morphology of W18O49 nanowires and their electrochromic properties

In wet-chemistry processes, pH value is an important parameter that can be used to control the microstructures of the as-grown nanostructures . In this work, W 18 O 49 nanowires with crystalline@amorphous core-shell structures were synthesized by controlling the pH of the precursor solutions in a hydrothermal reaction . Due to surface functionalization by ethylene glycol (EG) groups, the hydrothermally grown W 18 O 49 nanowires could be easily dispersed in aqueous environment, thus enabling the fabrication of electrochromic thin films of W 18 O 49 nanowires by a simple spray-drying process. The optimized W 18 O 49 nanowire films showed a large optical modulation (ΔT) of 81.1% at 633 nm, short response time (coloring/bleaching time τ c /τ b  = 7.9 s/3.9 s), good cycle stability (ΔT retention was 84.5% after 1000 cycles), and the excellent memory effect (the color withstood for 36000s after turning off the voltage). Furthermore, the electrochromic device (ECD) (4 × 4 cm 2 ) based on the W 18 O 49 nanowires exhibits a large optical modulation of 56.6%, short response time (τ c  = 7.6 s, τ b  = 2.7 s), and superior coloration efficiency (CE) of 64 cm 2  C −1 . Finally, by simply amplifying the developed processes, a large-area electrochromic device (10 × 10 cm 2 ) was successfully prepared, which implies the possibility of large-area spraying process for practical applications.