A self-healing polyacrylic acid-based hydrogel electrolyte for flexible quasi-solid-state electrochromic device

Due to the demand for healing damages caused during applications, it is desired to develop self-healing hydrogel electrolytes for flexible electrochromic device (ECD). A hydrogel electrolyte with remarkable self-healing ability, outstanding stretchability, and high ionic conductivity is presented in this work. Non-covalent interactions such as ionic connections between Ca2+ and -COO-, as well as numerous hydrogen bonds between PAA and HPMC, form dynamically cross-linked PAA-HPMC-Ca hydrogel electrolytes. Owing to the exceptional reversibility of non-covalent interactions, the hydrogel electrolyte exhibits remarkable self-healing and durability. Fracture strain and stress in the self-healed PAA-HPMC-Ca hydrogel can reach 429% and 240 KPa, respectively. In addition, a flexible ECD based on PAA-HPMC-Ca hydrogel electrolyte and a WO3 electrochromic layer was assembled and evaluated. The flexible quasi-solid-state ECD possesses excellent modulation transmittance range (approximately 66%), high coloration efficiency and steady response time. Thanks to the stability of the PAA-HPMC-Ca hydrogel electrolyte, the flexible ECD exhibits a great stability over 1000 cycles. This study may pave the way for self-healing electrolyte gels to be used in ECDs, supercapacitors, and batteries, among other flexible electrochemical devices.