Hexagonal phase NiS octahedrons co-modified by 0D-, 1D-, and 2D carbon materials for high-performance supercapacitor

It's crucial to improve the electronic conductivity, active sites and structural stability of transition-metal sulfides for better performance. Herein, hexagonal-phase NiS octahedrons were obtained through phase transition and co-modified by multidimensional carbon, i.e. 0D carbon QDs, 1D CNTs, and 2D reduced graphene oxide (NiS@C QDs-CNTs-rGO). It delivers a significantly enhanced specific capacity of 241 mAh g⁻¹ at a current density of 1 A g⁻¹ and capacity of 149 mAh g⁻¹ at 20 A g⁻¹, superior to its counterparts with other phases NiS₂@CNTs-rGO (154 mAh g⁻¹ at 1 A g⁻¹, 52 mAh g⁻¹ at 20 A g⁻¹) and Ni₇S₆@CNTs-rGO (167 mAh g⁻¹ at 1 A g⁻¹, 124 mAh g⁻¹ at 20 A g⁻¹). Furthermore, asymmetric supercapacitors (ASC) assembled by NiS@C QDs-CNTs-rGO and graphene hydrogel achieve a remarkable cycling stability (capacity retention of 82% after 5000 cycles). XPS results confirm that strong C–S bonds exist between carbon matrix and NiS NPs, which stabilizes structural stability and thus leading to excellent long-term cycling stability. The excellent electrochemical performance could be ascribed to the improved conductivity and structural stability, the co-modified 0D, 1D, and 2D carbon structures, and strong C–S bonds between active material and carbon matrix.