Fabrication of uniform urchin-like N-doped NiCo2O4@C hollow nanostructures for high performance supercapacitors

Abstract

Transition metal oxides are commonly used in electrochemical energy storage materials, but there are still many drawbacks that impede a wide range of applications. Heteroatom doping can significantly improve its performance. Herein, we have successfully prepared highly uniform N-doped NiCo₂O₄@C hollow nanostructures for supercapacitors by a two-step hydrothermal treatment associated with successive annealing process. Prepared N-doped NiCo₂O₄@C materials exhibited an admirable specific capacitance of 1028 F g⁻¹ at a current density of 3 A g⁻¹, with 625 F g⁻¹ remaining even at high current density of 20 A g⁻¹. Besides, this composite showed good electrochemical stability with capacity retention of 84% after 5000 cycles repetitive galvanostatic charge–discharge test at 10 A g⁻¹. An asymmetric supercapacitor was assembled by the N-doped NiCo₂O₄@C electrode, attached activate carbon (AC) as a counter electrode, exhibiting a high energy density of 26.67 W h kg⁻¹ at a power density of 402 W kg⁻¹. The improvement of electrochemical performance is ascribed to the co-doping of nitrogen and carbon atoms. These results indicate that N-doped NiCo₂O₄@C can be employed as an ideal electrode material for electrochemical energy storage.