Design and preparation of a ternary composite of graphene oxide/carbon dots/polypyrrole for supercapacitor application: Importance and unique role of carbon dots

A ternary composite of graphene oxide/carbon dots/polypyrrole (GO/CDs/PPy) used as electrode active material for supercapacitor has been synthesized via in situ polymerization of GO/CDs with pyrrole under a mild condition. The CDs sandwiched between GO film and PPy layer can promote electron transportation in the ternary composite and thus reduce the internal resistance and charge transfer resistance of the electrode. Additionally, the CDs with large specific surface area can enhance the interfacial property among GO, CDs and PPy and increase the dielectric constant of the ternary composite. Notably, GO/CDs/PPy exhibits a specific capacitance of 576 F g−1 at a current density of 0.5 A g−1, and a supercapacitor fabricated by two symmetric GO/CDs/PPy electrodes owns a high energy density of 30.1 Wh kg−1 at a power density of 250 W kg−1. More importantly, the as–fabricated supercapacitor can keep an excellent cycle stability after 5000 cycles. In practice, a simple device assembled by five supercapacitors in series could power 59 light–emitting diode indicators for more than 60 s after only charging for 17 s. This work demonstrates that CDs can play an important and unique role in improving performance of a hybrid electric double layer capacitor (EDLC)/pseudocapacitor.