Controllable synthesis of hierarchical NiCo2S4@Ni3S2 core–shell nanotube arrays with excellent electrochemical performance for aqueous asymmetric supercapacitors

Abstract

In this study, unique NiCo₂S₄@Ni₃S₂ core–shell nanotube arrays (NTAs), a promising positive electrodes for supercapacitors, have been successfully synthesized on Ni foam via a novel method. Electrochemical tests show the highest area specific capacity of 4.25 C cm⁻² at 4 mA cm⁻², maintained at 3.12 C cm⁻² at 40 mA cm⁻². In addition, a 3D reduced graphene oxide (rGO) aerogel has been fabricated as a negative electrode for supercapacitors, and this displays an excellent capacitance performance of 286.9 C g⁻¹ at 1 A g⁻¹. An asymmetric supercapacitor denoted as NiCo₂S₄@Ni₃S₂//rGO has been assembled based on NiCo₂S₄@Ni₃S₂ core–shell NTAs and rGO aerogel. The NiCo₂S₄@Ni₃S₂//rGO device achieves an outstanding performance with a specific capacity of 163.15 C g⁻¹, an energy density of 32.75 W h kg⁻¹ at a power density of 0.36 kW kg⁻¹. Moreover, it displays a remarkable cycling performance (77.5% capacity retention after 5000 cycles). These results indicate potential applications of NiCo₂S₄@Ni₃S₂//rGO in asymmetric supercapacitors (ASCs).