Grafting engineering of ZIF-8 and polymer to enhance performance of gel electrolyte in electrochromic devices

As an indispensable and crucial component in electrochromic devices, transparent gel electrolyte has a significant impact on optical contrast, switching speed, cycling stability, and mechanical robustness. In this study, an engineering by grafting polar bimolecular groups of Terephthalic Dihydrazide (TPHD) onto the surface of ZIF-8 nanoparticles and polymer to enhance performance of gel electrolyte was proposed. Benefiting from the stable pore structure and high dispersion of TPHD modified ZIF-8 (TPHD@ZIF-8), the gel electrolyte doped with 6 wt% TPHD@ ZIF-8 (TGPL-6 %) achieves high initial transmittance of 82 % at 633 nm, representing a 23 % enhancement over the 6 wt% unmodified ZIF-8 doped gel polymer electrolyte layer (ZGPL-6 %). A high ionic conductivity of 1.73 mS/cm was obtained, which was 30 % higher than that of ZGPL-6 % (1.33 mS/cm) and more than four times that of pure GPL (0.37 mS/cm). Young's modulus and tensile strength of TGPL-6 % are 0.0064 and 0.179 MPa, respectively. The TGPL-6 % has been successfully applied in electrochromic devices, achieving a high optical modulation of 38 % and excellent durability. This work provides valuable insights into the rational design of high-performance transparent gel electrolytes for advanced electrochromic devices.