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High-Performance Ni-Co Sulfide Nanosheet-Nanotubes Grown on Ni Foam as a Binder Free Electrode for Supercapacitors

The novel hierarchical Ni-Co sulfide nanosheet-nanotubes arrays were directly grown on Ni foam, as binder-free electrodes, have been successfully synthesized following a one-step facile hydrothermal method combined with a sulfide treatment. The initial value of the area capacitance achieved 2.28 F cm−2 at a current density of 1 mA cm−2. A high areal capacitance retention of 95.2% compared to activation-induced peak value is achieved after 3000 charge-discharge cycles, which is much better than counter Ni-Co oxide electrode (1.75 F cm−2 at 1 mA cm−2, 93.2% retention compared to activation induced peak value). The outstanding and excellent super capacitive performance is ascribed to ion-exchange reaction, which induces a flexible hollow nanotube feature and show higher conductivity, compared with Ni-Co oxide NWs. Cyclic voltammetry (CV) and Electrochemical impedance spectra (EIS) results confirmed that the synthesized electrode contains the lowest resistance at high, and at lower frequency, leading to easy penetration of electrolytes and fast transportation of electrons inside the electrode. In this proposed work, a one-step hydrothermal method has been followed, and provided for the sulfide-induced, with a noticeable electrochemical performance of nickel cobaltite compounds and supplying a promising route for high-performance supercapacitor electrodes.