Nitrogen-doped carbon dots anchored NiO/Co₃O₄ ultrathin nanosheets as advanced cathodes for hybrid supercapacitors

Herein, we demonstrate an advanced cathode of nitrogen-doped carbon dots (NCDs) anchored NiO/Co₃O₄ ultrathin nanosheets for hybrid supercapacitors by a facile hydrothermal-calcination route. Owing to the well defined thin-plate structure and ternary composition, the optimized NiO/Co₃O₄/NCDs nanosheets demonstrate a high specific capacity of 976.3 C g^-1 (1775 F g^-1) at 1 A g^-1, and a splendid cycling stability of approximately 95.7% retention over 10,000 continuous cycles (15 A g^-1). In addition, a hybrid supercapacitor is constructed by using NiO/Co₃O₄/NCDs nanosheets as cathode and reduced graphene oxide (RGO) supported NCDs composites as anode. The obtained NiO/Co₃O₄/NCDs//RGO/NCDs hybrid supercapacitor delivers a maximum energy density of 41.6 Wh kg^-1, together with outstanding cycling stability (no decay after 10,000 cycles at 10 A g^-1). Therefore, the ultrathin sheet-like structured NiO/Co₃O₄/NCDs cathode presents a great potential for supercapacitor application.