Enhanced electrochemical stability of carbon quantum dots-incorporated and ferrous-coordinated polypyrrole for supercapacitor

Carbon quantum dots-incorporated and ferrous-coordinated polypyrrole (CQDs/PPy-Fe) was designed as active electrode material of supercapacitors to improve electrochemical stability of PPy. The CQDs/PPy-Fe was prepared by incorporating CQDs into PPy-Fe which was formed through electropolymerization of ferrous chloride-coordinated pyrrole monomer. The ferrous-coordinated pyrrole monomer-kept tetrahedron structure could restrain volume swelling or shrinkage of PPy during the charge/discharge process, accordingly leading to improved cycling stability. In addition, the modification of CQDs could enhance the electrical conductivity of PPy and further improved rate capability of PPy. Specifically, CQDs/PPy-Fe showed lower capacity decay ratio of 45.4% than PPy (59.1%) from 1.0 to 20.0 A g−1. The capacitance retention ratio after 2000 cycles of CQDs/PPy-Fe and PPy was 94.6 and 79.4% at 20.0 A g−1, respectively. Moreover, symmetrical supercapacitor based on CQDs/PPy-Fe exhibited high capacitance and cycling stability. The design of CQDs/PPy-Fe presents the promising supercapacitor application for electrochemical energy storage.