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In this study, we report novel NiSe@MoSe nanosheet arrays prepared by a facile one-step hydrothermal method through nickel (Ni) foam as Ni precursor and the framework of MoSe. Owing to the unique interconnection and hierarchical porous nanosheet array architecture, the NiSe@MoSe nanosheet arrays exhibit a high specific capacitance of 774 F g at the current density of 1 A g, which is almost 2 times higher than that (401 F g) of the NiSe matrix and about 7 times greater than that (113 F g) of the MoSe nanoparticles. Moreover, we report an asymmetric supercapacitor (ASC), which is fabricated by using the NiSe@MoSe nanosheet arrays as the positive electrode and the graphene nanosheets (GNS) as the negative electrode, with aqueous KOH as the electrolyte. The NiSe@MoSe//GNS ASC possesses an output voltage of 1.6 V, an energy density of 25.5 Wh kg at a power density of 420 W kg, and a cycling stability of 88% capacitance retention after 5000 cycles. These results indicate that the NiSe@MoSe nanosheet arrays are a good electrode for supercapacitors.

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Herein, a novel asymmetric supercapacitor (ASC) with high energy density is fabricated based on the NiSe@MoSe2 nanosheet arrays and the nitrogen-doped pomelo mesocarps-based carbon nanosheet (N-PMCN) as a positive electrode and a negative electrode, respectively. The novel NiSe@MoSe2 nanosheet arrays are designed and prepared by a facile one-step hydrothermal growth method from nickel foam as a nickel precursor and nucleation framework. The N-PMCN is prepared using simultaneous CaCl2 activation and urea nitrogen-doped processes from thepomelo mesocarps as a biomass-based carbon precursor. Because of the unique nanosheet array architecture of NiSe@MoSe2 and interconnected sheet-like porous morphology with high nitrogen content (∼9 wt %) of N-PMCN, they exhibit a maximum specific capacity of 128.2 mAh g–1 and high specific capacitance of 223 F g–1 at a current density of 1 A g–1. Moreover, the assembled novel NiSe@MoSe2//N-PMCN ASC device with a maximum operating voltage of 1.65 V has demonstrated a high energy density of 32.6 Wh kg–1 at a power density of 415 W kg–1 and outstanding cycling stability with 91.4% capacitance retention after 5000 cycles in aqueous electrolyte.

Here, we report a novel type of nitrogen-doped porous interconnected carbon nanosheets derived from an easily gained and green plant-waste (pomelo mesocarps) by simultaneous activation, carbonization and nitrogen-doped processes using CaCl2 as activating agent and urea as nitrogen source. The nitrogen-doped pomelo mesocarps-based nanosheet carbon (N-PMNC) displays an interconnected sheet-like morphology, a high specific surface area (974.6 m 2 g-1), a porous architecture and a high nitrogen doping content (9.12 wt%). The N-PMNC based supercapacitor exhibited superior electrochemical performance with high specific capacitance of 245 F g-1 at 0.5 A g-1 and excellent rate capability (72% capacitance retention ratio even at 20 A g-1) in 2 mol L-1 KOH electrolyte. Furthermore, N-PMNC based symmetric supercapacitor possesses high specific energy of 14.7 Wh kg-1 at a power density of 90 W kg-1 operated in the wide voltage range of 1.8 V in aqueous neutral Na2SO4 electrolyte, and shows outstanding cyclic stability.