Shape controlled growth of hierarchical NixSy on stainless steel by solution processing with enhanced electrochemical energy storage performance

Abstract

Although a wide variety of multidimensional electrode materials have been developed for supercapacitors to greatly enhance their charge storage properties, the methods used to control their morphologies have typically been expensive, involve multiple steps, and require an annealing temperature, as well as a binder for electrode preparation. In this study, a cost-effective, single-step chemical route was used to grow hierarchical, multidimensional structures of nickel sulfide (Ni_xS_y) on a cheap and readily available stainless steel substrate (SS). The XRD results indicate that the crystallinity of the deposited material was strongly affected by the growth temperature. Films prepared at 90 °C exhibited the Ni₃S₄ crystalline phase, whereas at 100 °C, the NiS₂ phase was observed. The surface morphology of the Ni_xS_y/SS changed from a vertically aligned, rod-like morphology to a honeycomb or web-like surface as the growth temperature was increased from 70 °C to 100 °C, which ultimately influenced its electrochemical performance. Electrodes based on Ni_xS_y/SS films prepared at 70 °C, 80 °C, 90 °C, and 100 °C delivered specific capacitances (C_s) of 285, 141, 287, and 566 F g⁻¹, respectively, at a scan rate of 5 mV s⁻¹ in a 1 M KOH electrolyte. The galvanostatic discharge curves also revealed that the electrode prepared at 100 °C demonstrated excellent energy storage performance with an enhanced specific capacity (14 mA h g⁻¹), energy density (8.9 W h kg⁻¹), and power density (506 W kg⁻¹), which is attributed to the large specific surface area (3.147 m² g⁻¹) provided by the 3D web-like morphology of the electrode.