Self-supported α-Ni(OH)2 nanosheet arrays modified with carbon quantum dots for high-performance supercapacitors

In this paper, self-supported and binder-free α-Ni(OH)2 nanosheet arrays decorated with carbon quantum dots (CQDs/α-Ni(OH)2) are prepared using one-step hydrothermal method. The optimal electrode exhibits high specific capacitance of 1724.0 F/g at 3 A/g, which is 2.3 times higher than the 750.7 F/g of bare α-Ni(OH)2. 45.8% of capacitance retention rate is achieved with the current density increasing from 3 to 50 A/g. Hierarchical structure of α-Ni(OH)2 and the assistance of CQDs endow CQDs/α-Ni(OH)2 with enhanced reactive sites and improved electrical conductivity, achieving high electrochemical performance. Asymmetric supercapacitors assembled with CQDs/α-Ni(OH)2 and activated carbon (AC) deliver a high-energy density of 44.0 Wh/kg at 3000 W/kg and retain an energy density of 29.03 Wh/kg at 18,015 W/kg. 99.91% of the initial capacitance and 99.46% of the Coulombic efficiency are maintained after 5000 cycles at 10 A/g. This study provides a new approach to design high-performance electrodes for supercapacitors.