Preparation of Nickel Cobalt Sulfide Hollow Nanocolloids with Enhanced Electrochemical Property for Supercapacitors Application.
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ABSTRACT:
SUBMITTER: Chen Z
PROVIDER: S-EPMC4844973 | biostudies-other | 2016 Apr
REPOSITORIES: biostudies-other
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Project description:High energy density is still difficult to achieve using existing metal sulfides because of their low specific capacitance. To improve capacitance, a series of nickel and cobalt metal sulfides with different Ni/Co ratios were synthesized by a two-step hydrothermal method. Using the combining method of experimental research and first-principles calculation, the morphology, structural stability, electronic structure and electrochemical properties of metal sulfides were investigated systematically. The results show that the morphology of metal sulfides gradually grows from two-dimensional structure to nanotube arrays, and finally to nanorod arrays, as the Ni/Co ratios decrease. Among them, the NC24 sample with the Ni/Co ratio of 1 : 2 is a hollow nanotube array composed of NiCo2S4, which shows excellent electrochemical performance. The specific capacity of the NC24 sample reaches 1527C g-1 at 1 A g-1, and the capacity retention is 93.81% at 10 A g-1 after 2000 cycles. Furthermore, a symmetrical supercapacitor assembled from the NiCo2S4 nanotube array shows a high energy density of 67.5 W h kg-1. This strategy develops a nanotube array of metal sulfides and expands its application in a high energy density supercapacitor.
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Project description:A lightweight, flexible, and highly efficient energy management strategy is highly desirable for flexible electronic devices to meet a rapidly growing demand. Herein, Ni-Co-S nanosheet array is successfully deposited on graphene foam (Ni-Co-S/GF) by a one-step electrochemical method. The Ni-Co-S/GF composed of Ni-Co-S nanosheet array which is vertically aligned to GF and provides a large interfacial area for redox reactions with optimum interstitials facilitates the ions diffusion. The Ni-Co-S/GF electrodes have high specific capacitance values of 2918 and 2364 F g-1 at current densities of 1 and 20 A g-1, respectively. Using such hierarchical Ni-Co-S/GF as the cathode, a flexible asymmetric supercapacitor (ASC) is further fabricated with polypyrrple(PPy)/GF as the anode. The flexible asymmetric supercapacitors have maximum operation potential window of 1.65 V, and energy densities of 79.3 and 37.7 Wh kg-1 when the power densities are 825.0 and 16100 W kg-1, respectively. It's worth nothing that the ASC cells have robust flexibility with performance well maintained when the devices were bent to different angles from 180° to 15° at a duration of 5 min. The efficient electrochemical deposition method of Ni-Co-S with a preferred orientation of nanosheet arrays is applicable for the flexible energy storage devices.
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Project description:Metal-organic frameworks, as a kind of advanced nanoporous materials with metal centers and organic linkers, have been applied as promising electrode materials in energy storage devices. In this study, we are successfully prepared cobalt sulfide nanosheets (CoS) derived from the metal-organic framework on nickel foam (NF). The prepared electrodes are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller and Barrett-Joyner-Halenda and electrochemical methods like voltammetry, galvanostatic charge-discharge curve and electrochemical impedance spectroscopy. The CoS/NF electrode demonstrates a high specific capacity of 377.5 mA h g-1 (1359 C g-1) at the current density of 2 A g-1, considerable rate performance and excellent durability (89.4% after 4000 cycles). A hybrid supercapacitor is assembled using CoS/NF as the positive electrode and activated carbon as the negative electrode, it shows a high energy density of 57.4 W h kg-1 at a power density of 405.2 W kg-1. The electrochemical results suggest that the CoS nanosheet arrays would possess excellent potential for applications in energy storage devices.
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