Electrochemical Capacitor Based on Reduced Graphene Oxide/NiS2 Composite

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 (R) 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.

Automated summary

This study investigates the use of pyrite-like structure transition metal dichalcogenides (TMDs) NiS2 in electrochemical capacitors and the preparation of reduced graphene oxide (rGO) as a substrate for NiS2 deposition. The study analyzes the influence of pH on the structural and textural properties of rGO and compares the electrochemical response of rGO samples from different pH solutions. The results show that the addition of 5 wt% NiS2 significantly improves the capacitive response, and an asymmetric cell with rGO/5 wt% NiS2 as the positive electrode and rGO pH 12 as the negative electrode achieves high capacitance and electrochemical efficiency.