Construction of strawberry-like Ni3S2@Co9S8 heteronanoparticle-embedded biomass-derived 3D N-doped hierarchical porous carbon for ultrahigh energy density supercapacitors

The design of advanced supercapacitors requires electrode materials that combine high surface area with a developed hierarchical porous structure to facilitate ion transport and electrolyte permeability. Herein, we report a cross-linking and in situ sulfuration strategy for synthesizing nickel sulfide (Ni3S2) nanocrystal-attached cobalt sulfide (Co9S8) encapsulated on three-dimensional (3D) N-doped hierarchical porous carbon (Ni3S2@Co9S8/N-HPC). The Ni3S2@Co9S8/N-HPC composite was extensively studied using different characterization technologies. The results revealed that the obtained material integrated the advantages of a developed N-doped carbon framework (fast ion transport and excellent electrical conductivity) and transition metal sulfide species (high theoretical specific capacitance). Benefiting from the synergistic effect of a strawberry-like Ni3S2@Co9S8 structure and 3D interconnected hierarchical porous carbon, the resulting Ni3S2@Co9S8/N-HPC composite exhibited an ultrahigh attractive specific capacitance of 1970.5 F g(-1) at a current density of 0.5 A g(-1) and excellent cycling stability with a capacitance retention of 89.5% after 5000 cycles at 10 A g(-1). In addition, an asymmetric supercapacitor (ASC) of Ni3S2@Co9S8/N-HPC//HPC was assembled in a 6 M KOH electrolyte. It delivered an energy density of 77.1 W h kg(-1) at a power density of 263.3 W kg(-1), and it remained as high as 36.1 W h kg(-1) even at 25.9 kW kg(-1). It is believed that the presented work opens up a new strategy to fabricate high-performance supercapacitor electrodes.