Sulfur-deficient CoS/NiSnanoflakes anchored on N-doped graphene nanotubes as high-performance electrode materials for asymmetric supercapacitors

In this paper, Co9S8/Ni3S2 nanoflakes（NFs） with sulfur deficiencies were grown in-situ on N-doped graphene nanotubes（NGNTs）. They were successfully prepared through electrodeposition followed by hydrogenation treatment, which is able to act as a self-supported electrode for asymmetric supercapacitors（ASCs）. Combining the defect-rich active materials with highly conductive skeletons, the hybrid electrode N-GNTs@sd-Co9S8/Ni3S2NFs show ultrahigh specific capacity of ～304 mA hg-1 and prominent rate capability(capacity retention ratio of ～85% even at 100 Ag-1), and deliver a long cycling lifespan of ～1.9%capacitance loss after 10000 cycles. In addition, an ASC was constructed using the as-synthesized composite electrode as the positive electrode and active carbon（AC） as the negative electrode. The fabricated device shows a high energy density of～45.1 Wh kg-1 at ～3.4 kW kg-1 and superior cycling stability. This work substantiates a smart strategy to fabricate novel composite electrode materials for next-generation supercapacitors by incorporating riched deficiencies into nanostructures.