Spinel-type FeNi2S4 with rich sulfur vacancies grown on reduced graphene oxide toward enhanced supercapacitive performance

Abstract

Herein, the reduced graphene oxide (rGO)-based FeNi₂S₄ electrode material with rich sulfur vacancies (r-FeNi₂S₄-rGO) was prepared through a facile solvothermal procedure, followed by reduction with NaBH₄. During the NaBH₄ treatment, some sulfur atoms are removed from the lattice of FeNi₂S₄ and richer sulfur vacancies are generated, which can facilitate the transfer of electrons and decrease the equilibrium electron cloud density. In addition, the rich sulfur vacancies can enhance the intrinsic conductivity and increase the active sites, and the introduction of rGO can shorten the path of electron transfer, thus effectively boosting the electrochemical properties of the electrode material. Due to the coexistence of rich sulfur vacancies and rGO, the r-FeNi₂S₄-rGO electrode exhibits an excellent specific capacitance of 746.8 C g⁻¹ at 1 A g⁻¹. Moreover, an asymmetric supercapacitor assembled with r-FeNi₂S₄-rGO and active carbon (r-FeNi₂S₄-rGO//AC) shows an outstanding energy density of 43.4 W h kg⁻¹ at 800 W kg⁻¹ and cycling performance with 87.1% capacity retention at 4 A g⁻¹ after 1000 cycles, making it an excellent electrode material for supercapacitors. This study offers an effective strategy for the design and optimization of spinel-type sulfide electrode materials.