Ionic side-chain engineering in conjugated polyelectrolytes for high-performance pseudocapacitors

초록

Conjugated polyelectrolytes (CPEs) are promising materials for pseudocapacitor electrodes due to their redox-active backbones and tunable ionic functionalities. Here, we investigate the impact of ionic pendant groups on electrochemical performance by comparing anionic CPE-K (sulfonate-functionalized) and cationic CPE-Br (quaternary ammonium-functionalized), both featuring identical conjugated backbones. The opposite charge polarity influences how polarons are stabilized: notably, CPE-K undergoes self-doping due to its anionic sulfonate groups, while CPE-Br remains neutral. In their pristine states, CPE-Br exhibits a higher specific capacitance (95 F g-1vs. 84 F g-1), more distinct redox features, and better rate capability than CPE-K. This is attributed to its cationic nature, which prevents self-doping and enhances anion penetration from the electrolyte. Electrochemical impedance spectroscopy further corroborates these findings, revealing significantly lower charge-transfer resistance and a smaller Warburg factor for CPE-Br, indicative of faster ion diffusion compared to CPE-K. Upon forming composites with single-walled carbon nanotubes (SWCNTs), both materials exhibit enhanced performance; notably, the 2 : 1 CPE-Br/SWCNT composite outperforms its CPE-K counterpart, achieving a high specific capacitance of 291 F g-1 at 1 A g-1 and retaining 254 F g-1 at 5 A g-1. Furthermore, it demonstrates excellent cycling stability over 1000 cycles with similar to 99% coulombic efficiency, underscoring its robust charge storage reversibility and long-term durability. These findings highlight the importance of pendant group design in optimizing ionic transport and redox behavior in CPE-based pseudocapacitor systems.

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