Boosting PEDOT energy storage with a redox anthraquinone dopant for a flexible hydrogel supercapacitor at sub-zero temperatures

Although electrically conductive hydrogels based on conductive polymers hold promise for flexible and high-performance supercapacitors, it is still a challenge for such devices to maintain high capacitance with temperature change, especially under subzero conditions. Herein, conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) decorated with redox-active anthraquinone-2-sulfonic acid sodium (AQS) on the surface is homogeneously dispersed in a poly(acrylic acid) (PAA) hydrogel, which reinforces the conductivity and the stretchability of the obtained AQS–PEDOT/PAA hydrogel electrode. Particularly, with the containing of the H2SO4 + KCl electrolyte, the hydrogel is temperature tolerant and endows the assembled supercapacitor with a wide working temperature of −30 to 90 °C. Due to the extra energy storage contribution of AQS, the device exhibits a high capacitance of 466.5 mF cm−2, a maximum energy density of 41.47 μW h cm−2 and an exceptional cyclic stability of 90% retention after 5000 cycles. Very interestingly, the AQS–PEDOT/PAA electrode shows a remarkable solar-thermal conversion, which significantly boosts the electrochemical performance of the device under subzero conditions. Under solar illumination, the device shows a capacitance enhancement of 39.6% at −30 °C as compared with the device in the dark. This work provides an innovative strategy to spur the sluggish performance of conductive polymer-based hydrogel supercapacitors for practical applications.