Ion-Conducting Membranes Based on Gelatin and Containing LiI/I₂ for Electrochromic Devices

Abstract

Ionic conducting membranes of gelatin plasticized with glycerol and containing LiI/I₂ have been obtained and characterized by X-ray diffraction measurements, UV-Vis-NIR spectroscopy, thermal analysis and impedance spectroscopy. The transparent (80–90% in the visible range) membranes showed ionic conductivity value of 5 × 10⁻⁵ S/cm at room temperature, which increased to 3 × 10⁻³ S/cm at 80°C. All the ionic conductivity measurements as a function of temperature showed VTF dependence and activation energy of 8 kJ/mol. These samples also showed low glass transition temperature of −76°C. Moreover the samples were predominantly amorphous. The membranes applied to small electrochromic devices showed 20% of color change from colored to bleached states during more than 70 cronoamperometric cycles.

Keywords:

• Electrochromic devices
• gel polymer electrolytes
• gelatin
• ionic conductivity

Acknowledgments

The authors are indebted to FAPESP, CNPq, CAPES, for the financial support given to this research.