Abstract
Electrochemically active organic materials are emerging as a low cost, naturally abundant and sustainable alternative to their metal-based counterparts. However, their usage in energy storage systems is mainly hindered by their poor conductivity, which results in capacitance fade upon cycling. Here, for the first time, we report redox-active xerogel composed of 2,5-dimethoxy-1,4-benzoquinone (DMQ) decorated on reduced graphene oxide (rGO) sheets via hydrothermal method as a high capacitance and long cycle life pseudocapacitive electrode. The DMQ not only provided the stable redox-active centers but also served as a spacer to avoid rGO sheet aggregation and led to a three-dimensional (3D) hierarchical electrode architecture. When binder-free 50 µm thick rolled film was tested as a pseudocapacitive electrode, it exhibited excellent capacitance of 650 F/g at 5 mV/s (780 F/cm3) in 1 M sulfuric acid, outperforming a large number of reported organic and inorganic electrodes. Most importantly, optimized electrodes showed excellent capacitance retention of 99% after 25,000 cycles at 50 mV/s. Density functional theory calculations are further used to understand the charge storage mechanism, preferred orientation of the adsorbed molecules, charge density distribution and density of states. Our combined experimental and theoretical findings demonstrate that careful selection of the conductive substrate, electrode architecture and organic molecules play a crucial role for high capacitance and long cycling performance.