Hollow carbon spheres anchored with nitrogen-doped carbon dots for high-performance supercapacitors

As an emerging class of electrode materials, carbon dots are able to provide large specific surface area, abundant active sites and plentiful pseudocapacitive groups, which can effectively improve the electrochemical performance of supercapacitors. Herein, nitrogen-doped carbon dots (NCDs) are anchored on hollow carbon spheres (HCS) to construct novel carbon-based composites (NCDs@HCS) with hierarchical porous structures. Compared to the original HCS, the optimal NCDs@HCS sample has an ultrahigh specific surface area of 2163 m2 g−1 and possesses superior capacitance characteristics, including a significantly increased specific capacitance of 314 F g−1 at 1 A g−1 and an excellent cycling stability with 99.44 % capacitance retention after 10,000 cycles in a three-electrode system. When applied as a symmetric supercapacitor, the NCDs@HCS composite exhibits an enhanced energy density of 37.9 Wh kg−1 at a power density of 900 W kg−1. Such a performance surpasses that of most other carbon-based materials. The outstanding electrochemical behaviors of NCDs@HCS benefit from the unique morphology of HCS and the rich electron-donating regions provided by NCDs, which facilitate the mass transport and charge transfer. This work offers a new strategy to design advanced porous carbons for efficient energy storage.