A color-changing hydrogel electrolyte utilizing redox indicator of sodium 4-diphenylamine sulfonate for electrochromic applications

To solve the problems of liquid electrolytes, such as easy leakage, unsafety, and narrow applicable voltage range, a polyacrylamide (PAM) hydrogel electrolyte with high transparency and ionic conductivity has been developed. With addition of a redox indicator, sodium 4-diphenylamine sulfonate (SDAS), a color-changing SDAS@PAM hydrogel electrolyte was obtained. The integration of the PAM hydrogel and SDAS into one layer enables the electrolyte to achieve reversible color changes between green and colorless in addition to the function of transporting ions. An electrochromic device (ECD) based on the resulting color-changing hydrogel electrolyte was constructed with a configuration of FTO/ [email protected] /WO 3 · x H 2 O/FTO, where WO 3 · x H 2 O film was used as the counter electrode. A reversible color change between the superimposed blue-green color to colorless, a large optical modulation (74.2 %), fast responses (6.3 s for coloration and 11.8 s for bleaching) and a good cyclic stability are achieved. Additionally, the synergistic electrochromic effect of SDAS and WO 3 · x H 2 O can significantly reduce the coloration and bleaching voltages of the ECD. Therefore, our strategy of designing ECDs with a color-changing hydrogel electrolyte utilizing a redox indicator paves the way for developing and constructing more energy-efficient smart windows.