Li_xNa_2-xW₄O₁₃ nanosheet for scalable electrochromic device

Area of Science:

• Materials Science
• Nanotechnology
• Electrochemistry

Background:

• Printed electronics rely on functional inks with well-dispersed active materials.
• Two-dimensional (2D) materials offer superior properties but often require organic solvents or surfactants for dispersion.
• Limited dispersibility of 2D materials in aqueous solutions restricts their application in sustainable electronics.

Purpose of the Study:

• To develop a method for dispersing sodium tungstate (Na2W4O13) nanosheets in pure water for printed electronics.
• To investigate the properties of the aqueous ink and the resulting films for electrochromic applications.
• To fabricate and evaluate a flexible electrochromic device using the developed ink.

Main Methods:

• A lithium (Li)-ion exchange method was employed to modify Na2W4O13 nanosheets.
• The dispersity of the modified nanosheets in pure water was assessed using zeta potential measurements.
• Aqueous ink was prepared and spray-coated onto substrates to form uniform films.
• A complementary electrochromic device was assembled using Li-ion exchanged Na2W4O13 nanosheets and Prussian white.

Main Results:

• The Li-ion exchanged Na2W4O13 (LixNa2-xW4O13) nanosheets exhibited stable dispersity in water with a zeta potential of -55 mV.
• Uniform LixNa2-xW4O13 nanosheet films were successfully fabricated via spray coating.
• The electrochromic device demonstrated a large optical modulation (75% at 700 nm), fast switching (<2 s), and excellent cyclic stability.

Conclusions:

• The Li-ion exchange method effectively enhances the aqueous dispersibility of Na2W4O13 nanosheets.
• The developed aqueous ink is suitable for fabricating large-scale, flexible electrochromic devices.
• This approach holds significant potential for practical applications in smart devices and displays.