Cathodic Deposition of Metal Sulfide Nanostructures As Active Materials for High-Performance Supercapacitors

Supercapacitors (SCs) have been widely recognized in a wide range of energy storage applications over the past decade due to their higher specific power density, faster charge/discharge rates and longer cycle life compared to batteries. Hydrous ruthenium oxide (RuO₂) has been the most promising material with the high specific capacitance (>720 F g^-1). However, the low abundance and high prices restrict the application of RuO₂ in SCs. Hence, several alternatives have been proposed to be capable of the RuO₂such as metal oxide and conducting polymer. In addition, nanostructured metal sulfides have been widely investigated as SCs electroactive materials. In recent years, nanostructured metal sulfides have been widely synthesized by chemical precipitation and hydrothermal. Nevertheless, the aforementioned metal sulfides still needed polymer binder, conducting agent and high pressure coating on the conductive substrate, which could contribute extra contact resistance. In this way, electrodeposition seems to be a great approach to prepare the electroactive materials on conductive substrates since the active materials can be directly growth on substrates without using any polymer binder, conducting agent and high pressure, and the weight and thickness of electroactive materials can easily controlled by adjusting the deposition conditions.

In this study, cobalt sulfide and nickel sulfide nanostructures can be directly grown on Ni foam substrate as electroactive materials for high-performance supercapacitors by simply using a facile potentiodynamic deposition method. The Ni₃S₂ and CoS electrodes showed a high specific capacitance as well as 717 F g⁻¹ at 2 A g⁻¹ and 1471 F g⁻¹ at 4 A g⁻¹, as shown in Fig. 1(a) and Fig.1(b). As a result, nickel sulfides and cobalt sulfides can be considered as promising electrode materials for high-performance supercapacitors.