Partial Ion-Exchange of Nickel-Sulfide-Derived Electrodes\nfor High Performance Supercapacitors

Abstract

A novel\nmethod to adjust the composition of a material while maintaining\nits morphology was described in this study. Nickel sulfide, the material\ninvestigated in this work, was found to be useful as a high surface\narea electrode material for supercapacitor applications. First, a\nnest-like Ni₃S₂@NiS composite electrode with\n1D nanorod as structural unit was synthesized by simultaneously using\nNi foam as template and Ni as a source through a one-step <i>in situ</i> growth method. Co and Se ions, which respectively\nacted as beneficial cation and anion, were successfully introduced\ninto the nest-like Ni₃S₂@NiS material, resulting\nin the formation of Ni₃S₂@Co₉S₈ and NiS@NiSe₂ composite electrodes with structures\nsimilar to those of the parent materials. The material structure was\nvirtually retained and single-crystal-to-single-crystal transformation\nwas achieved in the process. Introducing the cation and anion into\nthe same type of material while maintaining topology could be important\nfor the field of material synthesis and preparation of supercapacitor\nelectrodes. Moreover, the electrochemical properties of these three\nmaterials were studied by cyclic voltammetry measurements and galvanostatic\ncharge–discharge tests. The results indicated that the rate\nperformance was improved significantly by ion exchange. In particular,\nthe derived electrode with Se still showed superior oxidation and\nreduction ability at high scan rate of 10000 mV s^–1. In addition, the second charge–discharge specific capacity\nalso increased from 516 F g^–1 to 925 F g^–1 and 1412 F g^–1 at the current density of 0.5 A\ng^–1 and by Co and Se exchange, respectively. This\nwork contributes to the knowledge on electrode materials for supercapacitors\nand can provide good reference for the fabrication of desired materials.