Thionine Functionalized 3D Graphene Aerogel: Combining Simplicity and Efficiency in Fabrication of a Metal‐Free Redox Supercapacitor

Abstract Discovering efficient pseudocapacitive charge storage materials has become one of the grand challenges to reduce the gap between high energy density batteries and high power density and durable electrical double‐layer capacitors. This research direction is facilitated by the introduction of redox‐active species that add Faradaic charge storage to the system. However, the astonishing abilities of organic redox species to increase energy density are insufficient to compensate for their poor electrical conductivity and inferior cyclability. Herein, it is proposed that these challenges can be simultaneously met by thoughtful selection of a redox species, thionine, that can be conjugated to a 3D graphene aerogel as a substrate via π–π interactions. The as‐fabricated metal‐free symmetric device exhibits a very high specific capacitance of 384 F g −1 at 1 A g −1 . Moreover, the device shows an ultrawide potential window of 2.0 V in pH‐neutral aqueous electrolytes and delivers a maximum specific energy of 32.6 Wh kg −1 , specific power of up to 12.8 kW kg −1 , outstanding flexibility, and an excellent capacitance retention of 91% after 10 000 charge–discharge cycles at 10 A g −1 . This device design provides an effective strategy to fabricate high‐performance aqueous supercapacitors and facilitates progress toward a sustainable energy future.