A study of fused-ring thieno[3,4-e]pyrazine polymers as n-type materials for organic supercapacitors

Conjugated polymer pseudocapacitors achieve high capacitances because they store charge through fast, reversible redox reactions. However, most of these polymers are only capable of storing charge in a ‘positive’ potential range, which results in low operating voltages and limited energy and power densities. The development of higher energy and power density polymer supercapacitors therefore hinges on the development of ‘negative’ charge-accepting pseudocapacitive materials to increase device operating voltages. Herein, we report the synthesis of a novel class of n-type pyreno[4,5-b]thieno[3,4-e]pyrazine (PTP) polymers. These polymers form the thickest films reported for reversibly negative and positive charge-accepting polymers synthesized by electrochemical oxidative polymerization. PTP polymers form porous films with capacitances of 6–14 F cm−3 at a current density of 0.5 A cm−3. The electrodes exhibit moderate cycling stability, with 42% capacitance retention after 200 cycles. This work demonstrates the first use of thienopyrazines (TPs) in energy storage applications, and provides guidelines for further improvements in the performance of n-type materials.