Green Fabrication of Agglomeration-Reductive and Electrochemical-Active Reduced Graphene Oxide/Polymerized Proanthocyanidins Electrode for High-Performance Supercapacitor

Reduced graphene oxide (rGO) has been regarded as a promising electrode material for supercapacitors. However, its application has been restricted by the corrosive reducing agent, inevitable structure agglomeration, and limited electric double-layer capacitor (EDLC) performance. Here, we develop a 3D redox-active rGO/polymerized proanthocyanidins hybrid for high-performance supercapacitance. Using a green and effective hydrothermal process, oligomeric procyanidins (OPCs) have acted as an eco-friendly reductant for GO reduction. It also worked as a polymeric proanthocyanidin (GSP) precursor for the enhancement of pseudocapacitance, where GSP acted as a spacer for inhibiting the agglomeration of rGO/GSP sheets and improving the total specific capacitance. As a result, the as-prepared rGO/GSP composites display a cooperative energy storage mechanism of an electrochemical double-layer capacitor (EDLC) and a pseudocapacitor, with an increased specific capacitance from 141 F g(-1) at 2 A g(-1) for the pure rGO to 402 F g(-1) at 2 A g(-1) for the rGO/GSP hybrids. Meanwhile, the rGO/GSP-based symmetrical supercapacitor provides a high specific capacitance of 185 F g(-1) at 0.8 A g(-1), an energy density of 25.8 Wh kg(-1) at a power density of 0.8 kW kg(-1), and a good cycling stability with 60.8% capacitance retention over 10000 cycles at 2 A g(-1). Such an excellent electrochemical performance comes from the agglomeration reduction structure and synergistic effects between the highly conductive graphene and pseudocapacitive GSP.