Electrochromic behavior of WO3 nanoplate thin films in acid aqueous solution and a protic ionic liquid

• Tungsten oxide nanoplates were obtained by one spot sonochemical method.
• Electrochromic films were prepared by electrophoretic deposition.
• Electrochromic performance in acid and protic ionic liquid was investigated.
• Limited amount of water in PIL avoids film dissolution.

WO3 nanoplates were synthesized in non-aqueous solvent using a one-step process ultrasonic irradiation. The nanostructured morphology was maintained in the films prepared by electrophoretic deposition (EPD) process onto ITO substrates. Spectroelectrochemical experiments were carried out by using both, H2SO4 and a protic ionic liquid (PIL) N-methyl-pyrrolidinium tetrafluoroborate, electrolytes. Cyclic voltammograms (CVs) were combined with transmittance measurements for all films that undergo typical reversible color change from colorless to blue. The integrated cathodic current of intercalation/deintercalation was used to calculate the coloration efficiency (CE) of films; the value obtained being in good agreement with nanostructured WO3 films. The coloration/bleaching processes showed good color efficiency, fast coloration time and optical contrast in acid electrolytes. The results using PIL as electrolyte, instead of H2SO4, show that all electrochromic parameters were improved, including the cyclic durability that was higher in this medium. Therefore, the use of a PIL enables proton intercalation but no dissolution suggesting its use as a suitable electrolyte for electrochromic devices.

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