Carbon Dots Doped with Ni(OH)₂ as Thin-Film Electrodes for Supercapacitors

Nickel hydroxide (Ni(OH)2) is one of the most attractive electrode materials for supercapacitor applications due to its intrinsically high redox capacitance. However, the electrochemical performance of the film electrode decreases dramatically with the increase in the Ni(OH)2 loading amount, which severely obstructs its large-scale use for supercapacitors. In this work, carbon dots (CDs) in situ doped Ni(OH)2 thin-film electrode has been fabricated by a cathodic electrodeposition approach. During the electrodeposition process, CDs intervene in the stack growth of Ni(OH)2 crystal nuclei and create a Ball-packed porous structure different from the relatively dense aggregate for the undoped film electrode. Meantime, the size of the Ni(OH)2 nanocrystals for the CD-doped film electrode is about 5–10 nm, far less than that of 30–50 nm for the undoped electrode. This modified thin-film electrode presents higher electrical conductivity as well as electrochemical activity (155.57 mAh/g specific capacity at 40 A/g) than that reported recently. More importantly, the specific capacity difference between the doped and undoped electrode is increased with the loading amount, implying the good doping effect of CDs even for the electrode with a thicker film. In addition, the asymmetric supercapacitor, assembled from the Ni(OH)2-CDs and alternating current (AC) electrodes, shows 77.5 Wh/kg energy density when the power density is up to 45.0 kW/kg. This work actually provides a reference for fabricating a high-performance Ni(OH)2 electrode with both high electrochemical activity and large capacity.