Abstract
The process of sulfurization of nickel foam surfaces to obtain Ni 3 S 2 layers with high electrochemical capacitance and stability during electrochemical cycling has been extensively studied. However, the role of nickel hydroxide layers, which are expected to form under the electrochemical operating conditions of the Ni 3 S 2 /NF electrode, has not been sufficiently investigated. In the present work, it is demonstrated that the hydroxide phase makes a significant contribution to both electrochemical capacitance and cyclic stability. The Ni 3 S 2 /NF electrode was fabricated via a single–step hydrothermal method in the presence of thiourea at 160 °C. The initial structure of Ni 3 S 2 on the NF surface was subsequently modified through electrochemical cycling in a KOH electrolyte. The increase in electrochemical capacitance of the electrode was accompanied by the formation of multiple nickel hydroxide phases, as identified by X–ray diffraction (XRD) and Raman spectroscopy. The electrode exhibited high performance stability over 20,000 galvanostatic charge–discharge (GCD) cycles at a current density of 20 A g −1 , retaining 90% of its maximum capacitance. The specific capacitance of the Ni 2 S 3 electrode was 758 F g −1 at a current density of 2.7 A g −1 . When the current density increased to 90 A g −1 , the specific capacitance decreased to 233 F g −1 , corresponding to 30% of the capacitance at 2.7 A g −1 .