Revealing Energy Density in Porous Carbon Supercapacitors Using Hydroquinone Sulfonic Acid as Cathodic and Alizarin Red S as Anodic Redox Electrolytes

Exploration of innovative strategies aiming to boost energy densities of supercapacitors without sacrificing the power density and long-term stability is of great importance. Herein, highly porous nitrogen-doped carbon spheres (NPCS) are decorated onto the graphite sheets (GSs) through a hydrothermal route, followed by a chemical activation. The capacitive performance of the NPCS is then enhanced by hydroquinone sulfonic acid (HSQA) incorporation in both cathodic electrolyte and electrode materials. Later, NPCS are decorated with polypyrrole (PPY), in which HSQA takes a versatile role as conjugated polymer dopant and cathodic redox additive. The capacitive performance of the negative electrodes is enhanced by incorporating of alizarin red S (ARS) as anodic redox additive. Finally, PPY(HQSA)@NPCS-GS//NPCS-GS asymmetric supercapacitor is assembled and tested in dual redox electrolyte system containing HQSA-cathodic and ARS-anodic electrolytes. This device delivers a remarkable energy density of 60.37 Wh kg^-1, which is close or even better than lead acid batteries. Thus, the present work provides a novel pathway to develop high energy supercapacitors using redox active electrolytes for next-generation energy storage applications.