Supramolecular engineering of cathode materials for aqueous zinc-ion hybrid supercapacitors: novel thiophene-bridged donor-acceptor sp(2) carbon-linked polymers

Rechargeable aqueous zinc-ion hybrid supercapacitors (Zn-HSCs) are promising candidates as large-scale energy storage devices owing to their high electrochemical performance, safety, long life, and low price. The development of nanostructured electrode materials featuring multiple active sites capable of interacting with Zn ions represents an efficient strategy to boost their electrochemical performance. In this work, we report for the first time the use of donor-acceptor carbon-linked conjugated polymers (DA-CCPs) as cathodes in aqueous Zn-HSCs. We have synthesized two novel DA-CCPs via Knoevenagel polymerization between electron-accepting 2,2 ',2 ''-(benzene-1,3,5-triyl)triacetonitrile and electron-donating 2,5-thiophene dicarboxaldehyde or [2,2 '-bithiophene]-5,5 '-dicarboxaldehyde, yielding DA-CCP-1 and DA-CCP-2, respectively. DA-CCP-2, which possesses an extra-thiophene unit in the backbone, exhibits improved electrochemical characteristics when compared to DA-CCP-1, and performance surpassing those of other reported cathode materials for aqueous Zn2+ energy storage systems. DA-CCP-1 and -2 based electrodes exhibited an outstanding energy density of 80.6 and 196.3 W h kg(-1) respectively, representing the highest value ever reached for conjugated polymers to date. This study not only offers new perspectives for the rational design and precise synthesis of DA-CCPs but it also broadens the choice of cathodes for high-performance aqueous Zn-HSCs.