Extending the π-Conjugated Benzoimidazoisoindolone-based n-Type Ladder Polymers: Highly Air-robust Aqueous Sodium-ion Electrochromic Energy Storage and Mechanism

Abstract

Electro-active conjugated polymers have already exhibited their prominent advantages in the field of electrochromic energy storage materials (EESMs) in recent years. However, achieving highly air-stable n-type conjugated polymers EESMs in aqueous electrolytes remains an enormous challenge. This present demonstrates the first investigation of benzoimidazoisoindolone-based n-type fully conjugated ladder polymers (BBL-EC and BAL-EC) for EESs, featuring high electron affinity, efficient and reversible electrochemical redox activity, high electron/ion conductivity, and an extended conjugated backbone structure. These polymers demonstrate enhanced electrochromic performance using aqueous sodium-ion as electrolyte under atmosphere, alongside high optical contrast and exceptional cycling stability. The optical contrast of BAL-EC was 53.8% at 740 nm, and remained unchanged after 1200 cycles owing to the extending π-conjugated structure. Furthermore, BAL-EC exhibited a high specific capacitance of 257.22 mAh g -1 . Electrochromic energy storage mechanism of benzoimidazoisoindolone-based conjugated polymers: sequential electron transfer involving preferential carbonyl reduction followed by imidazole ring reduction enables synergistic regulation of color switching and energy storage. Benzoimidazoisoindolone-based n-type fully conjugated ladder polymers demonstrate promising potential for highly air-stable aqueous sodium-ion electrochromic energy storage systems.