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A simple hydrothermal route is designed to decorate NiCo 2 S 4 nanoparticles on the surface of N-doped carbon nanotubes to form a coaxial composite (NiCo 2 S 4 @NCNT). Inherited the high electrical conductivity from the NCNT and high capacitive performance of NiCo 2 S 4 , the optimized NiCo 2 S 4 @NCNT composite could significantly reduce the contact resistance and effectively increase the transfer rate of ion and electron and thus benefit for its electrochemical performance enhancement. When employed as a battery-type supercapacitor electrode, the NiCo 2 S 4 @NCNT composite exhibits a high capacitance up to 783.5 C g −1 at 1 A g −1 and as well as rate performance (74.6% retention with the current density increases from 1 to 50 A g −1 ). Coupled with activated carbon (AC) negative electrode, the as-assembled hydride supercapacitor delivers a maximum energy density of 49.75 Wh kg −1 at a power density of 774.65 W kg −1 , as well as 88.9% capacitance retained after 3000 cycles at a current density of 10 A g −1 . These above results demonstrate the enormous potential of NiCo 2 S 4 @NCNT in the development of hybrid supercapacitors. [ABSTRACT FROM AUTHOR]

A current collector of reduced graphene oxide modified Ni foam (RN) is synthesized through a handy method of hydrothermal. The sheet-like reduced graphene oxide (rGO) wrapped around the skeleton of Ni foam establishes a unique structure of the current collector with large surface area as well as good electronic conductivity which make a positive effect on the promotion of electrochemical property. Pd is chosen as the catalyst and deposited on the RN substrate in a form of nanoparticle by potentiostatic electro-deposition. Characterization analysis including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and inductive coupled plasma emission spectrometer (ICP) are conducted to investigate the morphology and structure of the final electrode of Pd nanoparticles decorated rGO supported on Ni foam (PRN). In 2 mol L −1 NaOH and 0.5 mol L −1 H 2 O 2 , a current density of 450 mA cm −2 is gained on the PRN electrode which is much larger than that on the electrode of Pd nanoparticles directly deposited on Ni foam (PN). An excellent stability of the PRN electrode is also concluded by the measurements revealing that this material can be potentially and widely applied to direct hydrogen peroxide fuel cell in the near future. [ABSTRACT FROM AUTHOR]

• Carbon-coated SnS nanosheets and reduced graphene oxide composites are designed and synthesized. • Dual-carbon modification enhances the rate performance of SnS. • Potassiation stage adjustment results in stable cycling performance. Potassium ion batteries (PIBs) have attracted lots of attention due to its abundant resources. Exploring capable anode materials becomes one of the critical issues to achieve high-performance PIBs. Herein, carbon-coated SnS nanosheets and reduced graphene oxide (SnS@C/rGO) composite are designed and synthesized by a solvothermal reaction and heat treatment. The strategy of double carbon modification enhances the rate performance of SnS. Meanwhile, the cycling stability of SnS@C/rGO can be further improved by optimizing the voltage window, which can achieve the potassiation stage adjustment. K ions storage mechanism of SnS@C/rGO is investigated under different voltage windows. The deep alloying reaction occurs under low potential and is harmful to cycling performance. Moreover, the electrochemical kinetics of K ions storage is investigated by quantitative kinetics analysis. This work highlights the important effect of dual-carbon modification and adjusting the potassiation stage on the K ion storage. [ABSTRACT FROM AUTHOR]

• NiNb 2 O 6 @NC-2 hollow nanoparticles is used as rate capability anode for LICs. • The NiNb 2 O 6 @NC-2 exhibits a high specific capacity of 435.8 mAh g−1 at 50 mA g−1. • NiNb 2 O 6 decomposes into Ni metal and Li x Nb 2 O 6 in the 1st charge/discharge process. • The NiNb 2 O 6 @NC//AC LICs has a maximum energy density of 123.9 Wh kg−1. Searching for anode materials with fast Li+ intercalation kinetics to mitigate the dynamic imbalance with the rapid capacitive cathode is the fundamental strategy to achieve high energy-power density of Li-ion capacitors (LICs). Hence, NiNb 2 O 6 hollow nanoparticles are first synthesized by hydrothermal method and then sealed with a protective N-doped carbon shell to achieve the target NiNb 2 O 6 @NC composite. As the anode of LICs, the NiNb 2 O 6 @NC sample exhibits a high capacity of 435.8 mAh g−1 at 50 mA g−1 and excellent rate performance of 47.8% capacity retention with the current density increased to 2 A g−1. The lithium storage mechanism of NiNb 2 O 6 is proposed as a combined conversion reaction and an intercalation reaction, which the NiNb 2 O 6 decomposes into Ni metal and Li x Nb 2 O 5 during the 1st discharge/charge process. The irreversible Ni would not contribute to the reversible capacity and will improve the electric conductivity for fast transport of electrons and the Li x Nb 2 O 5 will act as the host for lithium ions by means of the intercalation mechanism. Furthermore, the assembled NiNb 2 O 6 @NC//activated carbon LICs exhibit a maximum energy density of 123.9 Wh kg−1 and the capacity retention reaches 86.1% after 5000 cycles. The superior electrochemical performances indicate that the rationally-designed NiNb 2 O 6 @NC is expected to be a potential anode material for LICs. [ABSTRACT FROM AUTHOR]

• The human hair with high elasticity capable can serve as a promising flexible supporter for the electrode. • The reduced graphene oxide nanosheets can effectively improve the electrical conductivity of the electrode. • The Ni(OH) 2 nanoribbon-intercalated rGO nanosheets shows an interconnected porous structure. • The solid-state flexible supercapacitor delivers high energy density and good cycling stability. The demands for wearable energy storage devices keep growing and novel flexible electrode materials and facile prepared methods for these devices are crucial and attractive. In this work, human hair fiber is employed as the flexible fiber-based material due to the high utilization values of low cost, controllable length and high elasticity capable. Herein, an effective and hazard-free microwave-assisted method is reported to develop superelastic reduced graphene oxide coating human hair (rGO@Hh) to achieve conductive and high-strength fibrous electrode. With the braided rGO@Hh fibers, nickel hydroxide nanoribbon-intercalated rGO nanosheets (Ni(OH) 2 /rGO@Hh) are further prepared through microwave radiation treatment, which shows an interconnected porous structure with outstanding electrochemical performances of high specific capacitance (316 F g−1 at 1 A g−1) and good cycling performance. Moreover, a solid-state fiber-based asymmetric supercapacitor (FASC) is assembled with rGO@Hh fibers and Ni(OH) 2 /rGO@Hh fibers as negative and positive electrodes, which demonstrates a high energy of 27.6 Wh kg−1 and a power density of 699 W kg−1, respectively. The FASC also can be further used for numerous electronic products, presenting its prospect for portable wearable devices with high tensile strength and excellent performances. [ABSTRACT FROM AUTHOR]