Different controlled nanostructures of Mn-doped ZnS for high-performance supercapacitor applications

Various Mn-doped ZnS controlled nanostructures were synthesized directly on the nickel foam to develop a binder-free, high-performance positive electrode for supercapacitors, where specific energy, specific power, and cycling stability are the crucial parameters. We achieved Mn-doped ZnS based different nanostructures, such as nanosheets, nanoflakes, and nanoneedles just by monitoring the reaction temperature. Among those three morphologies, the nanosheets showed the highest specific capacitance of 1905 F g−1 at a current density of 1 A g−1 and 93.1% capacity retention after 10,000 cycles in a three-electrode system. An asymmetric supercapacitor (ASC) device was assembled using Mn-doped ZnS nanosheets and activated carbon as a positive and negative electrode, respectively. The ASC device showed a high capacitance of 140 F g−1 (210 C g−1), delivered a high specific energy of 43.3 Wh kg−1, and a high specific power of 6.8 kW kg−1. The ASC device retained 93.3% with excellent coulombic efficiency of 95.7% after 8,000 cycles. Importantly, two serially connected ASC devices illuminated 52 red light-emitting diodes. This highlights the potential of the Mn-doped ZnS based ASC device for the next generation supercapacitors.