NiCo2S4 nanosphere anchored on N, S co-doped activated carbon for high-performance asymmetric supercapacitors

Abstract

Throughout the evolution of supercapacitors, binary transition metal sulfides have been extensively researched for their potential as electrode materials. Here, NSAC-NiCo₂S₄ composites are prepared by in-situ growing NiCo₂S₄ nanosphere on N, S co-doped activated carbon (NSAC) using a simple solvothermal way. The optimized NSAC-NiCo₂S₄ composite inherits the NSAC’s huge specific surface area, hierarchical porous structure, and high electronic conductivity, along with the excellent capacitive performance of NiCo₂S₄. This combination effectively reduces contact resistance and enhances the transfer rate. Calculations based on the density functional theory further indicate that synergistic interactions between NiCo₂S₄ and NSAC in the composite lower the OH⁻ adsorption energy and release more active electrons. This enhancement facilitates the electrochemical reaction kinetics in supercapacitors. The as-fabricated NSAC-NiCo₂S₄-2 electrode possesses a remarkable specific capacitance (762 F g⁻¹) at 1 A g⁻¹ and exhibits a minimal charge transfer resistance (0.28 Ω)_. Furthermore, an asymmetric supercapacitor (positive electrode: NSAC-NiCo₂S₄-2; negative electrode: NSAC), achieves an impressive energy density of 36.6 Wh kg⁻¹ at a power density of 400.0 W kg⁻¹. It also exhibits exceptional cycling stability, maintaining 86.2 % of its capacity after 10,000 cycles. These excellent results further highlight the great potential of the obtained NSAC-NiCo₂S₄ composites for use in energy reserve systems.