A carbon quantum dot decorated RuO2 network: outstanding supercapacitances under ultrafast charge and discharge

Carbon quantum dots (CQDs) due to their unique properties have recently attracted extensive attention from researchers in many fields. In the present work, a new application in the form of a CQD-based hybrid as an excellent electrode material for supercapacitors is reported for the first time. The CQDs are fabricated by a facile chemical oxidation method following which they are thermally reduced, and further decorated with RuO2 to obtain the composites. The hybrid exhibits a specific capacitance of 460 F g(-1) at an ultrahigh current density of 50 A g(-1) (41.9 wt% Ru loading), and excellent rate capability (88.6, 84.2, and 77.4% of capacity retention rate at 10, 20, and 50 A g(-1) compared with 1 A g(-1), respectively). Surprisingly, the hybrid shows exceptional cycling stability with 96.9% capacity retention over 5000 cycles at 5 A g(-1). Such remarkable electrochemical performances can be primarily ascribed to the significantly enhanced utilization of RuO2 achieved by the efficient dispersion of tiny reduced CQDs and the formation of a CQD-based hybrid network structure that can facilitate the fast charge transport and ionic motion during the charge-discharge process. Additionally, the contact resistance at the interface between active materials and current collectors is concluded to be a key factor in determining the performance of the hybrid. These results above demonstrate the great potential of CQD-based hybrid materials in the development of high-performance electrode materials for supercapacitors.