Rational Design of the 1,4<i>-</i>Diaminobenzene-Functionalized Benzoquinone Cross-Linked Polymer Electrode Material for a High-Performance Flexible Supercapacitor Device

Redox-active polymers have been investigated for fabricating flexible and wearable electrochemical energy storage (EES) devices. However, the core issues restricting the preparation of conjugated redox polymers in practical supercapacitor (SC) devices are its solubility in electrolyte solvents, poor ion mobility, inferior rate capability, and difficulty in processing. Our main motivation in the present work was to prepare a cross-linked polymer as an alternative to a linear polymer, which is soluble and mechanically unstable, and study its EES properties. Here, we report a molecular-engineered new donor–acceptor–donor cross-linked polymer BAPh-BQ-AC based on 1,4-diaminobenzene (DAPh) and benzoquinone (BQ) that exhibits several accessible redox-active sites for fast faradaic reversible processes. First, the as-fabricated BAPh-BQ-AC/graphite foil (GF) electrode in the three-electrode SC device was investigated. Based on the results of the three-electrode SC, we used BAPh-BQ-AC/(GF) for further charge storage testing in a two-electrode symmetric SC device. BAPh-BQ-AC/(GF) showed impressive pseudocapacitive behavior in both types of SC devices in an aqueous 1 M H2SO4 electrolyte solution. Further, a flexible symmetric supercapacitor (FSSC) device was fabricated using the BAPh-BQ-AC/graphite foil (GF) electrode in a poly(vinyl alcohol) (PVA)/H2SO4 gel electrolyte. The FSSC cell is mechanically robust at 0 and 180° bending angles. The as-fabricated FSSC devices demonstrate a specific capacitance (Csp) of 102.39 and 99.59 mF cm–2 at 0 and 180° bending angles, respectively, at 0.5 mA cm–2 current density. At 2 mA cm–2, the FSSC cells exhibit a satisfactory Csp retention of 75.74% (0°) and 70.98% (180°) of their initial values after 5000 galvanostatic charging–discharging cycles, indicating superb mechanical flexibility. Moreover, at 0.5 mA cm–2, it exhibits an energy density of 17.90 μW h cm–2 at 1.76 mW cm–2 power density. The remarkable electrochemical and mechanical characteristics indicate that this novel BAPh-BQ-AC/(GF) electrode-based FSSC cell configuration is expected to contribute for the design and preparation of promising flexible and wearable electronics.