Electrochemical Capacitor Based on Reduced Graphene Oxide/NiS2 Composite

• Published in: ChemElectroChem Vol. 9; no. 21
• Main Authors: Kachmar, Andrii, Tobis, Maciej, Frąckowiak, Elżbieta
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 15.11.2022; Wiley-VCH
• Subjects: Capacitors; composite; Crystallites; electrochemical capacitor; Electrodes; Electronic structure; Graphene; Hydrothermal reactions; nickel sulphide; Pyrite; Raman spectroscopy; reduced graphene oxide; Substrates; Transition metal compounds; transition metal dichalcogenides
• ISSN: 2196-0216; 2196-0216
• DOI: 10.1002/celc.202200834

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. Symmetric cell assembled with hydrothermally reduced graphene oxide (rGO) shows capacitance of 134 F g−1 at 0.2 A g−1 for samples obtained at pH=12. NiS2 was deposited on the surface of the rGO during hydrothermal treatment. Due to catalytic activity of transition metal dichalcogenides (TMDs), asymmetric cell (−) rGO||rGO NiS2 (+) was assembled to avoid hydrogen evolution reaction. The cell exhibited capacitance of 164 F g−1 at 0.2 A g−1.