Amorphous nickel sulfide nanoparticles anchored on N-doped graphene nanotubes with superior properties for high-performance supercapacitors and efficient oxygen evolution reaction.

The rational design of a novel material system with superior properties of energy storage and conversion is a significant work. In this paper, amorphous nickel sulfide nanoparticles anchored on N-doped graphene nanotubes (N-GNTs@NSNs) were firstly synthesized by a facile electrochemical-deposition method, which can serve as free-standing robust supercapacitor electrode materials and electrocatalysts. Stemming from the disordered structure of amorphous active materials and the synergy of novel N-GNT framework materials, the as-prepared N-GNT@NSN electrode unveils prominent capacitive behaviors, including a large specific capacity of 240 mA h g-1 (2160 F g-1), decent rate capability, and outstanding cycling stability (95.8% of capacity retention after 12 000 cycles). An asymmetric supercapacitor with N-GNTs@NSNs as the positive electrode and active carbon (AC) as the negative electrode is further assembled, which shows a maximum energy density of 49.5 W h kg-1 at a power density of 800 W kg-1 and robust stability (96.6% capacity retention after 12 000 cycles). Moreover, the electrode also possesses high activities in the oxygen evolution reaction (OER), namely it can attain a current density of 10 mA cm-2 at an overpotential of 284 mV in 1 M KOH. This finding is not only important for significantly enhancing the electrochemical performances of supercapacitor electrode materials and electrocatalysts, but also lays the solid foundation for their further industrial applications in energy storage and conversion systems.