Synthesis of polypyrrole nanotubes@nickel-molybdenum sulfide core–shell composites for aqueous high-performance asymmetric supercapacitors

Abstract Transition metal sulfides have attracted extensive attention as promising electrode materials for advanced supercapacitors. However, their poor electronic conductivity and low utilization rate of the unfavorable structure still hinder energy-power outputting performance of supercapacitors. Herein, polypyrrole nanotubes@nickel-molybdenum sulfide (PNTs@NiMoS) core–shell composites were successfully synthesized via a one-step hydrothermal method in which honeycomb-like NiMoS nanoflakes were in-situ grown on the surface of PNTs. The introduction of PNTs with high conductivity as the core facilitates the rapid transportation of electrons and ions besides providing pseudocapacitance. And the in-situ grown NiMoS nanoflakes with special honeycomb-like as the shell provide much active sites accessible to electrolyte ions for charge storage. Owing to the synergistic electrochemical contributions from PNTs and NiMoS, the ratio-optimized PNTs@NiMoS exhibits the high specific capacitance of 1557.2 F g−1 at 1 A g−1, remarkably superior to NiMoS (885.1 F g−1), PNTs (172.2 F g−1) and other reported bimetallic sulfides-based electrode materials. Moreover, the assembled asymmetric supercapacitor in 6 M KOH electrolyte with PNTs@NiMoS as the positive electrode and N-doped carbon nanotubes as the negative electrode delivers a superior energy density of 35.8 Wh kg−1 at a significantly high power density of 13719.1 W kg−1, much higher than previously-reported similar supercapacitors. Furthermore, the asymmetric supercapacitor exhibits good cycling stability with the capacitance retention of 84.9% after 5000 cycles. This study offers a feasible strategy to design electrode materials with special microstructure for high-performance energy storage devices.