Acid- and alkaline-induced phase and structure reconstruction of nickel sulfide toward enhanced electrochemical performance

Abstract

Nickel sulfides prepared using conventional methods usually exhibit bulk structure and multiple phases, which pose great challenges for controllably synthesizing designer particles with high performance. Herein, we developed a novel and universal strategy to regulate the crystal phase and structure of nickel sulfide through an acid- or alkaline-induced strategy. We found that HCl and KOH could partially extract nickel and sulfur from nickel sulfide under a hydrothermal process, respectively. As a result, HCl treatment induced the transformation of nickel sulfide from nickel-rich phase (NiS) to nickel-deficient phase (NiS₂) and bulk structure to micro–nano structure. The KOH treatment induced the transformation of nickel sulfide from a sulfur-rich phase (NiS₂) to a sulfur-deficient phase (NiS), as well as the changes in surface microstructure. Attributed to the structural advantages brought by structure reconstruction, these samples exhibit enhanced electrochemical properties after the treatment. This is a unique and significant finding to the structure-regulation method of transition metal sulfides and will enrich their structure-dependent applications in supercapacitors or batteries.