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submitted on 18.08.2020 and posted on 19.08.2020by Mark Miltenburg, Nimrat Obhi, Bryony McAllister, Dwight Seferos
Pseudocapacitive polymers offer potential for higher energy densities than electrostatic double layer capacitive materials and lower cost than pseudocapacitive metal oxides. These polymers typically demonstrate good stability when storing positive charge but poor stability when storing negative charge. The power and energy densities of these materials is also limited when the operating voltage window is restricted to positive voltages. The development of polymers capable of stable positive and negative charge storage is necessary to allow a wider voltage window and create high performance polymer supercapacitors. Here we present a PEDOT-pendant tetrachlorinated perylene diimide polymer capable of storing positive and negative charge, which utilizes a donor-nodeacceptor architecture to prevent electronic interaction between positive and negative charge storing units. The polymer films show balanced charge storage and excellent stability in both positive and negative charge storage, retaining more than 80% of their capacitance over 1000 cycles. The films demonstrate moderate capacitances of 78.6 F g-1 in the positive region and 73.1 F g-1 in the negative region at 0.5 A g-1, as well as excellent rate capabilities in positive and negative charge storage regions of 87% and 56% at 20 A g-1, respectively. The polymer film was applied as both electrodes in a symmetric type III supercapacitor device with a gel polymer electrolyte, demonstrating a wide operating potential range of 2.2 V. These results demonstrate that the cycling stability of ambipolar polymers can be improved using a donor-node-acceptor polymer architecture with an extended π-conjugated donor unit.