Micro-controlling of the grain boundaries in NiCo2O4/NiCo2S4 nanowires for enhanced charge storage.

In this work, the micro-controlling of the grain boundaries in NiCo2O4/NiCo2S4 nanowire arrays was achieved by exposing them to a sulfur containing atmosphere at 300 °C with different exposure times. The results showed that the capacitance of the optimal NiCo2S4 sample reached 400 μA h cm-2 at 30 mA cm-2 with a current retention rate of 58.6%. The assembled NiCo2O4/NiCo2S4//activate carbon electrode delivered a capacitance of 299.2 μA h cm-2 and 241.7 μA h cm-2 at a current density of 3 mA cm-2 and 30 mA cm-2, respectively. The cycling tests showed a good current retention rate of 88.1% after 8000 cycles. Besides, the NiCo2O4/NiCo2S4 composite exhibited a power density of 480.1 W kg-1 at an energy density of 47.87 W h kg-1, and 4773.66 W kg-1 at 38.67 W h kg-1, which indicated its potential for practical applications.