High energy density hybrid supercapacitor based on cobalt-doped nickel sulfide flower-like hierarchitectures deposited with nitrogen-doped carbon dots

Abstract

The exploration of advanced electrode materials with outstanding electrochemical properties is of considerable importance for hybrid supercapacitors but challenging. In this paper, an effective two-step solvothermal route is demonstrated to synthesize nitrogen-doped carbon dots (NCDs) decorated cobalt-doped nickel sulfide (Co-NiS) flower-like hierarchitectures. Because of the modification with NCDs and doping by cobalt atoms, the resulting Co-NiS/NCDs hierarchitectures exhibit an ultrahigh specific capacity up to 1240 C g⁻¹ (2480 F g⁻¹) at 1 A g⁻¹ and a remarkable rate capability of 790.8 C g⁻¹ (1581.6 F g⁻¹) even at 20 A g⁻¹ when used as advanced electrodes for supercapacitors. More significantly, coupling with ap-phenylenediamine (PPD) modified reduced graphene oxide (rGO) anode, a hybrid supercapacitor device is successfully constructed, which possesses an impressive energy density of 71.6 W h kg⁻¹ at 712.0 W kg⁻¹ and a decent cyclic stability with 78.3% retention after 12 000 cycles at 5 A g⁻¹. The dual improvement strategy may provide insight to rational engineering of novel electrode materials with multi-components for high-performance hybrid supercapacitors.