Hydrochloric acid induced microstructural reconfiguration from bulk α-NiS microspheres to porous/hollow NiSx microspheres for high-performance hybrid supercapacitor

Abstract

Nickel sulfide is well known as a promising energy storage/conversion material considering its high redox activity, high theoretical capacity, easy preparation, and rich phase structures. Unfortunately, nickel sulfide prepared by conventional methods usually exhibits a bulk structure, which significantly limited its charge storage. To overcome this obstacle, we developed a facile hydrochloric acid-induced structure reconstruction strategy to fabricate porous and hollow structured nickel sulfide via a one-step hydrothermal process. We found that nickel sulfide undergoes de-nickelization in the presence of 3 M hydrochloric acid, resulting in the transformation from bulk structure to porous/hollow structures, accompanied by a transition from nickel-rich phase (α-NiS) to nickel-deficient phase (Ni3S4 or NiS2). The electrochemical results demonstrated the obviously improved specific capacity of nickel sulfide after structure reconstruction, among which the porous NS-HCl-1 h (α-NiS/Ni3S4) microspheres delivers the highest specific capacity (204.4 mAh g-1 at 1 A g-1) and show a rate performance about 50.0% from 1 to 20 A g-1. The assembled NS-HCl-1 h//rGO supercapacitor delivers a maximum energy density of 47.1 Wh kg-1 at a power density of 803.6 W kg-1, and maintain a capacity retention rate about 88.6% after 10,000 cycles. This work provides a novel method and contributes new insight for the structural reconstruction of transition metal sulfides (TMSs).