Mg²⁺-assisted hydrothermal growth of vertically-aligned Ni₃S₂ nanorod bundles on nickel foam for application as binder-free supercapacitor electrodes

Abstract

Vertically-aligned Ni₃S₂ nanorod bundles were grown on nickel foam through a novel hydrothermal method for application as supercapacitor electrode. In this method, Fe³⁺ ions were utilized as the etching agent for the nickel foam substrate; the nickel foam itself is both the nickel source for Ni₃S₂ and the scaffold substrate. Furthermore, it was revealed that Mg²⁺ ions can act as growth modifiers and afford vertically-aligned nanorod bundles of Ni₃S₂. A crystal growth mechanism was proposed and the vital roles of Fe³⁺ and Mg²⁺ were explained. Electrochemical studies of the Ni₃S₂ electrodes were conducted in 3 M KOH solution, and the cyclic voltammetric tests revealed that the charge storage of the Ni₃S₂ nanorod bundles involves both capacitive and charge-transfer mechanisms identified by high base currents and broad redox peaks, respectively. A specific capacitance of 230 mF cm⁻² at a high potential scan rate of 100 mV s⁻¹ with a stable performance up to 1000 cycles attests the superiority of the supercapacitor electrode.