Controlled synthesis of NiCo2S4 nanostructured arrays on carbon fiber paper for high-performance pseudocapacitors

A facile hydrothermal method is utilized to produce nanostructured NiCo2S4 arrays on carbon fiber paper with controlled morphologies to study the effect of morphology on their electrochemical performance in supercapacitors. Specifically, NiCo2S4 solid nanofiber, nanotube, and hollow nanoneedle of the same crystalline structure are synthesized by controlling the conditions of the hydrothermal synthesis. Among the three different morphologies studied, the hollow nanoneedle of NiCo2S4 shows the highest capacity and the longest cycling life, demonstrating a specific capacitance of ~1154 F g−1 at a charge–discharge current density of 1 A g−1 and negligible capacity loss after 8000 cycles (at a rate of 10 A g−1). This high performance is attributed to the unique nanostructure of the hollow nanoneedle, suggesting that the morphology of NiCo2S4 plays a vital role in determining the electrochemical performance. Further, an asymmetric capacitor consisting of NiCo2S4 hollow nanoneedle electrode and a tape-cast activated carbon film electrode achieves an energy density of ~17.3 Wh kg−1 at 1 A g−1 and a power density of ~0.2 kW kg−1 at 20 A g−1 in a voltage range of 0–1.5 V, implying that it has a great potential for a wide variety of practical applications.