Nickel-doped Co3O4 spinel nanospheres embedded in nitrogen-doped carbon composites derived from bimetallic NiCo metal–organic framework as a high-performance asymmetric supercapacitor

Abstract

In this work, nitrogen-doped porous carbon spheres (NCS) with Ni_xCo₃O₄ composite were derived from a metal–organic framework through a simple hydrothermal method followed by heat treatment. The composition and structure of the resulting Co₃O₄/NCS and Ni_x–Co₃O₄/NCS were regulated by the temperature treatment of nitrogen-doped porous carbon spheres (NCSs) with an organic ligand source. The materials were characterized using a variety of analytical methods such as FE-SEM, XRD, FTIR, XPS, HRTEM, and BET, respectively. The Ni_x–Co₃O₄/NCS-2 composite has a high surface area of 198 m² g⁻¹ and a pore volume of 4.85 cm³ g⁻¹. As-prepared Ni_x–Co₃O₄/NCS-2 electrode delivered a high specific capacitance value of 1284 F g⁻¹ at a current density of 1 A g⁻¹ with excellent cycling stability of 96.9% retention after 3000 cycles. Excellent electrochemical performance is due to the synergetic effect of the porous structure and nitrogen-doped carbon. Moreover, an asymmetric supercapacitor was built using Ni_x–Co₃O₄/NCS-2 as a positive electrode and MWCNT as a negative electrode, which delivered a maximum power density of 416.7 W kg⁻¹ at an energy density of 26.38 Wh kg⁻¹ with good cycling stability of 92% retention after 3000 cycles. The results demonstrate nitrogen-doped porous carbon spheres (NCS) with Ni_x–Co₃O₄ as a promising electrode material for high-performance supercapacitors.