Electrochemical activation behavior of Ni3S2/Co9S8 composite in supercapacitor

Ni 3 S 2 /Co 9 S 8 composite is synthesized with nanosheet-wrapped irregular structures. • CV activation process and mechanism of the composite is disclosed in KOH solution. • CV activation induces the formation of well-defined hierarchical spherical structure. • The activated product presents a maximum capacitance of 4.30 F cm −2 at 1 A g −1 . A free-standing Ni 3 S 2 /Co 9 S 8 composite with nanosheet-wrapped irregular structures is fabricated on nickel foam (NF) framework. Compared with pristine Ni 3 S 2 , the specific capacitance of Ni 3 S 2 /Co 9 S 8 increases to 2.62 F cm −2 from 1.99 F cm −2 , confirming a superior electrochemical activity of the composite. To further enhance the electrochemical performance and reveal the electrochemical activation behavior of the Ni 3 S 2 /Co 9 S 8 composite, cyclic voltammetry (CV) activation strategy is employed by inducing the reconstruction of electrode materials in KOH solution. The CV activation triggers the dissolution of sulfur species and the formation of amorphous Ni/Co (oxy)hydroxides. The activated product achieves its maximum areal capacitance of 4.30 F cm −2 at 1 A g −1 after 200 cycles, resulting in a well-defined spherical structure consisted of interconnected ultrathin nanosheets. The capacitance enhancement can be ascribed to hierarchical spherical structure and the optimized composition, which provide abundant active sites and facilitate ion diffusion and charge transfer. When configured as an asymmetric supercapacitor, the device comprising the Ni 3 S 2 /Co 9 S 8 composite and activated carbon exhibits a specific capacitance of 175.6 F g −1 , and the highest energy density reaches 62.44 Wh kg −1 . The Ni 3 S 2 /Co 9 S 8 composite shows significant potential as a high-performance electrode material for advanced supercapacitor applications. A Ni 3 S 2 /Co 9 S 8 composite with a nanosheet-wrapped irregular morphology is grown on Ni foam. CV activation dissolves sulfur species and forms amorphous Ni/Co (oxy)hydroxides with a hierarchical spherical structure, achieving a maximum areal capacitance of 4.30 F cm −2 at 1 A g −1 . Download: Download high-res image (156KB) Download: Download full-size image