Covalently anchored benzimidazole-reduced graphene oxide as efficient electrochemical supercapacitor electrode material

Portable electronic devices have recently garnered significant attention in the realm of flexible energy storage technologies, as improving the energy density of supercapacitors while maintaining stability and high power density remains a considerable challenge. The simple processing of functionalization of graphene provides enormous possibilities for customizing its nanostructure and characteristics for energy storage capabilities. In this study, we present the pioneering synthesis of reduced graphene oxide (rGO) with the help of Delonix regia (DR) flower extract. Subsequently, rGO was subjected to functionalize with heterocyclic benzimidazole (BI) via a nucleophilic substitution reaction, resulting in the formation of the covalently structured BI-rGO nanocomposites, which serve as robust and highly efficient supercapacitor electrodes. The synthesized BI-rGO exhibited higher specific capacitance of 252 µF/g at 1 A g⁻¹ surpassing the performance of rGO (104 µF/g at 1 A g⁻¹) in 1 M H₂SO₄, as demonstrated by screen-printed carbon electrodes. Impressively, the BI-rGO electrode showcased excellent capacitance retention of 96.6% over 15,000 life cycling tests in a pseudocapacitance supercapacitor. Furthermore, the BI-rGO electrode exhibited a remarkable 2.4-fold increase in energy density compared to the rGO electrode. The introduction of heterocyclic functionalities of BI was found to exert a significant impact on the enhancement of supercapacitor performance. The symmetric supercapacitor device of BI-rGO electrode achieved an areal capacitance of 163 mF cm⁻² at a current density of 1 mA cm⁻². Remarkably, this device yielded an energy density of 209 Wh cm⁻², accompanied by a power density of 1.6 W cm⁻². Furthermore, it revealed notable long-term cycling stability, sustaining 10,000 cycles at a fixed current density of 5 mA cm⁻² with a retention rate of 96.8%. These compelling results substantiate the potential of our supercapacitor for practical energy storage applications.