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Summary: Sodium‐ion hybrid capacitors are a prospective energy storage device candidate that couples the superiorities of battery‐type and capacitive storage mechanisms. In this study, we fabricate a composite of NiCo2O4 nanowires with carbon tubular bundles (CTBs) via a facile hydrothermal and annealing procedure. The density functional theory (DFT) calculations are performed to evaluate the bonding strength between the two components of the composite, the binding energy of the NiCo2O4 is calculated to be −0.952 J m−2, indicating that the NiCo2O4 nanowires can be stabilized on both sides of the carbon tubular bundles, which leads to a good cycling performance. Moreover, the composite in this work exhibits a metallic property because of the introduction of carbon material. As expected, when used for sodium storage, the NiCo2O4/CTBs shows a high capacity of 298 mA h g−1 at 1 A g−1 and high capacity retention of 92% after 500 cycles, which are superior than the bare NiCo2O4 electrode. Consequently, the sodium‐ion hybrid capacitor is also assembled with NiCo2O4/carbon tubular bundles and commercial activated carbon, which achieves high energy density of 99 Wh kg−1 in a wide potential range from 0.5 V to 4.0 V. [ABSTRACT FROM AUTHOR]

Developing novel materials with rational structures and excellent electrical conductivity is vitally important for energy storage devices. Herein, hollow cobalt molybdenum selenide (Co–Mo–Se) nanosheet arrays are fabricated via a self-sacrificing template method and selenization process, where cobalt-organic framework serves as the template. Benefiting from unique hollow nanoarrays structure, the Co–Mo–Se electrode offers rich electroactive sites, large accessible regions for electrolyte, and short ions diffusion pathways. Additionally, it is observed that the Co–Mo–Se possesses a low charge transfer resistance owing to the intrinsic metallicity. As a result, the Co–Mo–Se electrode exhibits favorable energy storage properties, including high capacity (221.7 mAh g−1), good rate property, and outstanding stability (95% after 8000 cycles). More importantly, the assembled Co–Mo–Se//active carbon (AC) achieves high energy density (44.7 Wh kg−1) and remarkable durability. Notably, two hybrid devices connected in series successfully power an electronic watch for 70 min, demonstrating its practical applicability. These results indicate that the synthesized hollow Co–Mo–Se nanosheet arrays have promising applications as electrode materials for high-performance energy storage devices. • Co-MOF was employed as template to obtain hollow Co–Mo–Se nanosheet arrays. • The Co–Mo–Se delivers a specific capacity of 221.7 mAh g−1 at 1 A g−1. • The ion exchange/etching method was applied in this work. • The asymmetric supercapacitor delivers high energy and power densities. [ABSTRACT FROM AUTHOR]

In this work, NiCo 2 S 4 , nickel-cobalt layered double hydroxides (NiCo-LDH) and CoS 2 electrodes are successfully prepared by using ZIF-67 as the precursor, the results show that NiCo-LDH and NiCo 2 S 4 are nano-flower-like structures and CoS 2 exhibits a nano-cage structure. The electrochemical properties of the hybrid supercapacitor assembled with NiCo 2 S 4 and activated carbon (AC) as electrodes were tested. As the positive electrode of NiCo 2 S 4 //AC hybrid supercapacitor, the NiCo 2 S 4 electrode has the largest specific capacity of 2934 mAh g−1 at a current density of 1 A g−1. The NiCo 2 S 4 //AC capacitor generates the highest energy density of 38.8 Wh kg−1 when the power density is 993.0 W kg−1 and has a nice cycling performance with a capacity retention rate of 81.2% after 10,000 cycles at 5 A g−1. • Nano-flower-like structures NiCo 2 S 4 is successfully prepared by using ZIF-67 as the precursor. • NiCo 2 S 4 shows nice performance as the cathode of NiCo 2 S 4 //AC (activated carbon) hybrid supercapacitor. • NiCo 2 S 4 //AC (activated carbon) hybrid supercapacitor shows practical potential. [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]

• Co 3 O 4 /Nitrogen-doped carbon (Co 3 O 4 /NC) composite was successfully prepared by a two-step calcination method with ZIF-67 as precursor. • The specific capacitance of Co 3 O 4 /NC at a current density of 1 A g−1 is 1144F g−1. • The Co 3 O 4 /NC//AC two-electrode capacitor generates the highest energy density of 40 Wh kg−1 at a power density of 1037 W kg−1. Metal-organic frameworks with high specific surface area and controlled morphology have great potential for lithium-ion battery applications. Here, the ZIF-67 precursor was prepared by the room temperature stirring method. Then Co 3 O 4 /NC composite electrodes with hollow polyhedral structure were successfully prepared by a two-step calcination method, and their electrochemical properties were discussed. The specific capacitance of Co 3 O 4 /NC at a current density of 1 A g−1 is 1144F g−1 (much higher than the specific capacitance of pure Co 3 O 4), and the retention rate is 45.4 % under a 20 A g−1 of current density. In addition, the asymmetric supercapacitor (ASC) device consisting of Co 3 O 4 /NC composite electrodes and activated carbon produced the highest energy density of 40 Wh kg−1 at a power density of 1037 W kg−1. At a current density of 5 A g−1, the capacitor retains 87.6 % of its initial capacitance after 10,000 charge/discharge cycles. [ABSTRACT FROM AUTHOR]

NiCoP/C electrodes with hollow structure are prepared successfully by solvent thermal method and low temperature phosphorylation method, the effect of Co doping on the electrode performance is explored. The hollow sphere structure of NiCoP/C electrode brings out outstanding electrochemical properties. The results of electrochemical tests show that the NiCoP/C electrode delivers a specific capacity of 193.8 mAh g −1 at 1 A g −1 and only losses 6.7% capacity under a 5 A g −1 of current density after 10,000 cycles. In addition, the asymmetric supercapacitor (ASC) device composed of NiCoP/C and activated carbon has an energy density of 53.7 W h kg−1 when the power density is 750 W kg−1. The ASC device is also cycled for 10,000 cycles at a current density of 5 A g −1 while the capacity loss is only 7.2%. [ABSTRACT FROM AUTHOR]

• α-MnSe Nanosheets are prepared via a facile hydrothermal method. • The effect of reaction time on electrochemical performance is investigated. • The α-MnSe electrode delivers a high capacity of 88.3 mAh g−1 at 1 A g−1. • The asymmetric supercapacitor exhibits a high energy density of 39.3 Wh kg−1. Transition metal selenides are regarded as emerging materials for energy storage devices because of their good electrical conductivity and electrochemical activity. Here, a binder-free ultrathin α-MnSe nanosheets electrode is prepared and the supercapacitor performance is comprehensively explored. Due to the increased active sites, enlarged contact area for electrolyte, as well as shorten ions diffusion pathway, the prepared electrode delivers high capacity of 88.3 mAh g−1 at 1 A g−1, good rate capability, and long-term durability (91% remain after 5000 cycles). Moreover, the asymmetric supercapacitor, fabricated by α-MnSe anode and active carbon cathode, displays a high energy density of 39.3 Wh kg−1 at a power density of 0.92 kW kg−1 and satisfying cycle performance. This study demonstrates that the binder-free α-MnSe electrode holds great promise for supercapacitor. [ABSTRACT FROM AUTHOR]