Electrochemical Capacitor Based on Reduced Graphene Oxide/NiS₂ Composite

Abstract

The use of a pyrite‐like structure transition metal dichalcogenides (TMDs) such as NiS2 is not reported as frequently as layered structured TMDs in electrochemical capacitors. Our study shows a reduced graphene oxide (rGO) preparation and its further use as a substrate for the deposition of NiS2 during the hydrothermal reaction. The influence of pH for the GO solution on the structural and textural properties of the resultant rGO was explained in detail by using Raman spectroscopy, UV, X‐ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen sorption at 77 K. The electrochemical response of the rGO samples obtained from various pH solutions was studied and compared in symmetric two electrode Swagelok® cells. As a result, rGO pH 12 was chosen for further modification with NiS2. The average size of the crystallites, and electronic structure of the rGO/NiS2 composite have been determined. The effect of the NiS2 content in the composite on the electrochemical results was further investigated. It occurred that 5 wt % NiS2 in the composite was sufficient for a significant improvement of the capacitive response. Interestingly, an asymmetric cell with rGO/5 wt % NiS2 working as a positive electrode and rGO pH 12 as a negative electrode was able to reach a high capacitance of 165 F g−1 at 0.2 A g−1 with 92 % coulombic and 79 % energetic efficiency.

Tuning the electrochemical properties of NiS2 2D-nanoflakes by one-zone sulfurization for supercapacitor applications

“…The presence of these nanoflakes is not observed for 200 °C and 400 °C sulfurization temperature. In different published works [23,[32][33][34][35], the NiS 2 -based 2D structures are reported to have high energy storage capabilities. Hence, these nanoflakes are strongly desirable to be present at supercapacitor structures.…”

“…Based on the SEM (figure 1), XRD (figure 2), and EDX analyses, the highest value of specific capacity is provided by the presence of the highest density of 2D-NiS 2 nanoflakes on the sample surface. It has been proven that the capacitive properties of 2D-structures based on NiS 2 are significantly higher compared to NiS [23,[32][33][34][35]. Therefore, it can be assumed that the dominant contribution to the capacitive behaviour of the NiS X samples originates from the presence of 2D NiS 2 nanoflakes.…”