8-Hydroxyquinoline-5-sulfonic acid on reduced graphene oxide layers as a metal-free electrode material for supercapacitor applications

Abstract Quinone organic materials are promising candidates to construct supercapacitor electrodes as they are entirely nontoxic, nonflammable, and safe for use. However, their wide adoption in supercapacitor applications is restricted by the inadequate electrical conductivity, which results in low mass and electron transfer, thereby leading to poor electrochemical performance. Herein, redox active 8-hydroxyquinoline-5-sulfonic acid (HQSA) compositing with reduced graphene oxide (rGO) through wet-chemistry method, as a high-performance electrode material is reported. Non-covalently interacted HQSA with rGO results in low internal resistance and high reversibility of the redox reaction. The as-prepared metal- and binder-free electrode in three-electrode cell configuration exhibits the specific capacity of 220C/g (61.1 mA h/g), demonstrating a 208% increase in capacity than bare rGO (105.5C/g or 29.3 mA h/g) at the same specific current of 0.5 A/g in 1 M H 2 SO 4 electrolyte solution. This electrode material shows an excellent cyclic stability with 99% capacity retention after 10,000 consecutive voltammetry cycles at 100 mV/s. Furthermore, a symmetrical two electrode cell was constructed, which endows maximum cell capacity of 45C/g (12.5 mA h/g) that is equivalent to a specific energy of 6.25 W h/kg and a specific power of 522 W/kg. This work not only provides a promising electrode for supercapacitor but more importantly demonstrates a unique strategy to design active and durable material for future energy storage technologies.