High electrochromic energy storage performance of polybenzimidazole isoindolinone-based n-type fully conjugated ladder polymers enhanced by H+/Zn2+ dual-ion synergistic effect

Conjugated polymer materials garner significant attention in the field of electrochromic energy storage because of advantages of tunable color properties, flexibility, lightweight nature, and high electrochemical activity. However, achieving an n-type conjugated polymers with high-performance electrochromic energy storage in aqueous and oxygen-containing environments remains a formidable challenge. In this work, poly(benzimidazobenzophenanthroline) (BBL) achieves high-performance n-type electrochromic energy storage via the rational molecular structure design of a fully conjugated rigid backbone and electrolyte optimization. The electrochemical behaviors, electrochromic properties, and pseudocapacitive energy storage characteristics of BBL are investigated in three aqueous electrolyte systems: 0.1 M H 2 SO 4 , H 2 SO 4 /ZnSO 4 (0.05 M/0.05 M), and 0.1 M ZnSO 4 /H 2 O. The results demonstrate that the H + /Zn 2+ dual-ion mixed electrolyte delivers synergistic benefits reflected by improved apparent ion-diffusion coefficients and accelerated interfacial reaction kinetics. The charge transfer resistance is as low as 25.59 Ω, which is significantly lower than that of the two single electrolyte systems. When utilizing the H + /Zn 2+ dual-ion mixed electrolyte, BBL achieves a favourable balance of electrochromic and energy-storage metrics. While this system exhibits a slightly lower optical contrast (ΔT = 16.74%) compared with the 0.1 M H 2 SO 4 electrolyte (ΔT = 17.88%), it affords much faster coloring/bleaching response times (3.9 s/3.7 s), superior long-term cycling retention (88.65% after 2300 cycles), and a high specific capacity of 121.9mA h g −1 at 0.1 mA cm −2 . This work proposes the modulation rules of the synergistic dual-ion effect on the dual functions of n-type conjugated polymers, laying a solid experimental and theoretical foundation for the rational design of high-performance aqueous electrochromic-energy storage bifunctional materials.