Enhanced electrochemical performance of polypyrrole depending on morphology and structure optimization by reduced graphene oxide as support frameworks

Abstract

Poor rate capability and cycling stability are the major bottlenecks which hinder the application of polypyrrole (PPy) as the supercapacitor electrode material. Herein, a series of nano-sheet PPy/reduced graphene oxide (rGO) composites are synthesized with rGO as support frameworks to optimize the morphology, specific surface area and electronic conductivity, consequently enhancing the rate capability and cycling stability. Voltammetric charge analysis and Peukert's equation are introduced to evaluate their capacitance performance. The results confirm that rGO obviously enhances the outer charge (up to 90% of the total charge), which is corresponding to the large outer electrochemical surface and rapid ion storage/release. Peukert's constant is determined with electrochemical impedance spectroscopy and the value for PPy/rGO-10 is close to the ideal value of 1 (1.02), implying a proximate ideal capacitive behavior. The large outer charge and proximate ideal capacitive behavior can greatly improve its capacitance performance, especially under rapid charging/discharging processes. Consequently, a high specific capacitance of 290 F g−1 is obtained for PPy/rGO-10 at 0.2 A g−1, retaining 247 F g−1 (85.2%) at 12.8 A g−1. Additionally, its capacitance retention of 97.5% can be achieved after 20000 cycles at a current density of 2 A g−1, exhibiting excellent cycling stability with a tiny over-oxidation degree increase.