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Ni 2 CoS 4 @(NiCo)Se 2 bimetallic selenides with core–shell heterostructure in-situ generated on Ni 2 CoS 4 nanorods arrays for high performance supercapacitors. [Display omitted] • Ni 2 CoS 4 @(NiCo)Se 2 composites with the core–shell structure are prepared by simple hydrothermal and in-situ selenization methods. • The synthesized electrode material exhibits good conductivity and a large specific surface area. • The assembled device has a high energy density (53 Wh kg−1) and power density (480 W kg−1). • Two assembled all-solid-state ASCs can light a 2.5 V LED lamp for 11 min. In this paper, Ni 2 CoS 4 @(NiCo)Se 2 /NF core–shell structural nanocomposites are successfully prepared on nickel foam (NF) substrates through a convenient hydrothermal method and tube furnace calcination. Firstly, NiCo 2 O 4 /NF is acquired by a one-step simple hydrothermal method and one-step tube furnace calcination, then it is sulfidated via a one-step hydrothermal method, and finally selenized by stirring to obtain Ni 2 CoS 4 @(NiCo)Se 2 /NF. The results show that in the three-electrode test, the specific capacitance of the Ni 2 CoS 4 @(NiCo)Se 2 electrode is able to reach 6054 mF·cm−2 at a current density of 10 mA·cm−2. The excellent performance of Ni 2 CoS 4 @(NiCo)Se 2 /NF nanocomposites is supposed to give rise to the bimetallic synergistic effect, as well as the unique core–shell structure of its surface-loaded nanosheets. In addition, all-solid-state asymmetric supercapacitors (ASCs) are composed of activated carbon (AC) as the anode and Ni 2 CoS 4 @(NiCo)Se 2 /NF as the cathode. The prepared Ni 2 CoS 4 @(NiCo)Se 2 /NF//AC ASC devices reach an energy density of 53 Wh kg−1 at a power density of 480 W kg−1. Simultaneously, Ni 2 CoS 4 @(NiCo)Se 2 /NF//AC ASC device has an excellent specific capacitance of 149.06F g−1 at a current density of 0.6 A/g and a capacitance retention rate of 84.0 % after 10,000 electrochemical cycles, which proves its good cycling stability. Impressively, two Ni 2 CoS 4 @(NiCo)Se 2 /NF//AC ASC devices connected in series can light up a 2.5 V LED lamp and continue to illuminate it for 11 min. Our results show that Ni 2 CoS 4 @(NiCo)Se 2 /NF nanocomposites with core–shell structures have great application potential in energy storage devices. [ABSTRACT FROM AUTHOR]

Hierarchical CoSe 2 @NiMn-LDH@Cu 1.8 Se/CF nanosheet arrays with core-shell structure are synthesized via phase pseudomorphic transformation process achieved by selective selenization for Cu and Co elements for green chemistry energy storage. [Display omitted] As an emerging energy storage device, the practical application of supercapacitors (SCs) is currently constrained by their low energy density. Enhancing the capacitance of supercapacitors by leveraging the synergistic effect of multiple components in composite electrodes with well-designed structures can effectively increase their energy density. Here, a wire-sheet-particle hierarchical heterostructured CoSe 2 @NiMn-layered double hydroxide (NiMn-LDH) @Cu 1.8 Se/Copper foam (CF) electrode is synthesized via phase pseudomorphic transformation process achieved by selective selenization for Cu and Co elements. Benefiting from the stable support structure of CuBr 2 , the large specific surface area of NiMn-LDH, and the excellent conductivity of CoSe 2 , the prepared binder-free electrode shows excellent electrochemical properties. The CoSe 2 @NiMn-LDH@Cu 1.8 Se hybrid electrode exhibits a superior specific areal capacitance of 7064 mF cm−2 at 2 mA cm−2 and a stable cyclic performance with 80.11 % capacitance retention after 10,000 cycles. Furthermore, the assembled CoSe 2 @NiMn-LDH@Cu 1.8 Se/CF//AC (activated carbon) asymmetric supercapacitor (ASC) achieves an energy density of 36.6 Wh kg−1 when the power density is 760.6 W Kg−1 and retains 87.35 % of the initial capacitance after 5000 cycles. Overall, this pioneering research provided new insight for preparing supercapacitor electrode materials by selective selenization and ration design of the structures. [ABSTRACT FROM AUTHOR]

[Display omitted] Ortho-hexagonal and highly-oriented NiMnCo-LDH/ZnO@CC self-supporting electrode derived from ZIF-67 covered ZnO nanorod-arrays is fabricated and employed for portable asymmetric solid-state supercapacitor. • Novel ortho -hexagonal NiMnCo-LDH has been synthesized. • ZIF-67 covered ZnO nanorod-arrays as self-supporting electrode is synthesized. • The fabricated electrodes exhibit superior electrochemical properties. • A multifunctional instrument can be powered for more than 30 mins. • The device can be carried outdoors to monitor time, temperature and air humidity. Metal-organic frameworks have attracted much attention due to their abundant redox sites and tunable characteristics, which are advantageous for energy storage applications. However, the low electrical conductivity, poor physical strength and undesirable capacity seriously hinder their applications. Therefore, designing effective and convenient strategies to build composites with unique structures will be of practical significance. Herein, we successfully generate NMC-LDH/ZnO@CC nanocomposites by growing ortho -hexagonal nickel–cobalt layered double hydroxide (NMC-LDH) nanosheets in-situ on ZIF-67 precursor covering vertical arrays of ZnO nanorods. As a result of the unqiue ortho -hexagonal structure, highly ordered arrangement of active substances and multi-dimensional spaces of the prepared NMC-LDH/ZnO@CC binder-free electrode, its capacitance is as high as 9258 mF cm−2 at a current density of 2 mA cm−2 and the capacitance retention is maintained at 87.5 % after 5000 cycles. Furthermore, in order to explore the practical value of the prepared binder-free electrode, the NMC-LDH/ZnO@CC//AC solid-state asymmetric supercapacitor device is assembled. The energy density of the assembled supercapacitor is 24.6 W h kg−1 at a power density of 170 W kg−1 and 1020 W kg−1 at an energy density of 11.8 W h kg−1. In addition, a versatile instrument for monitoring air humidity, time and ambient temperature in portable environments can be powered by a single ultracapacitor unit for more than 30 min. Overall, this study provides a unique strategy for synthesizing ZIF derivatives with novel morphologies for electrochemical energy storage applications. [ABSTRACT FROM AUTHOR]