Cross-linked electrodeposited conjugated polymers based on bis-thiophene-carbazole bis-adducts with an aromatic core for high performance supercapacitor electrodes

Abstract

Electrodeposited conjugated microporous polymers (CMPs) are attractive materials for energy storage as they can meet the key requirements of high capacitance, mixed electronic/ionic conductivities, and easy integration in (micro)storage systems. A series of conjugated bisadduct monomers combining bisthiophene-carbazole (BTC) units with various spacers between the carbazole moieties, including direct N–N linking (BBTC), phenyl (BBTC-Ph), its electron-deficient tetrafluorinated analogue (BBTC-TFB), and biphenyl (BBTC-BPh), is synthesized for electrochemical polymer deposition. The monomers and their corresponding polymers are studied to elucidate the influence of spacer units on electrochemical behavior, morphological features and porosity. PBBTC films reveal restricted accessibility to higher redox potentials requiring backbone planarization. BBTC-TFB exhibits donor–acceptor (D–A) type character, as evidenced by dual fluorescence, which hampers electropolymerization and results in poorly electroactive films. It is found that an extended phenyl/biphenyl core lowers the oxidation potential by ca. 0.2 V and affords cross-linked conjugated polymer films with a wider electroactive voltage window, higher coulombic efficiency and remarkably higher capacitance, owing to increased conjugation length, higher doping levels and improved ion diffusion within the porous structure. Both PBBTC-Ph and PBBTC-BPh films demonstrate enhanced areal capacitance, reaching 235 mF cm⁻² and 271 mF cm⁻² respectively, among the best reported values for polymer supercapacitor electrodes. The coulombic efficiency stabilizes above 99.8% after 1000 cycles. Furthermore, the films are able to withstand high current densities, as high as 10 mA cm⁻² for PBBTC-BPh. Thus, designing bisadduct-based CMP precursors with extended and electron-rich conjugated core linkers has emerged as a promising strategy for developing efficient electrogenerated energy storage materials.