Uniform growth of NiCo2S4 nanoflakes arrays on nickel foam for binder-free high-performance supercapacitors

In this work, ultrathin NiCo2O4 nanosheets have been synthesized through an electrodeposition method together with a further calcination process. By using CH3CSNH2 as sulfur source, the NiCo2O4 was converted into NiCo2S4 via anion exchange reaction (from oxygen to sulfur). Scanning electron microscopy imaging together with the energy-dispersive X-ray spectroscopy mapping indicates the successful transformation from NiCo2O4 to NiCo2S4. The uniform and porous NiCo2S4 architectures show good electrical contact to the current collector and good wettability, which can facilitate the transport for electrons and electrolyte ions. As a result, the as-prepared NiCo2S4 electrode shows a greatly enhanced electrochemical performance than NiCo2O4, with a high specific capacitance (1051 F g−1 at a current density of 0.5 A g−1) and good cycling stability (capacity retention of 85% after 5000 charge/discharge cycles). These impressive performances suggest that the porous NiCo2S4 structures can be used as promising binder-free electrode materials for high-performance supercapacitors.