Self-assembled synthesis of waxberry-like open hollow NiCo2S4 with enhanced capacitance for high-performance hybrid asymmetric supercapacitors

Engineering NiCo2S4 nanoparticles anchored on carbon nanotubes as superior energy-storage materials for supercapacitors

Fabricating high-capacity electrode materials toward supercapacitors has attracted increasing attention. Here we report a three-dimensional CNTs/NiCo2S4 nanocomposite material synthesized successfully by a facile one-step hydrothermal technique. As expected, a CNTs/NiCo2S4 electrode shows remarkable capacitive properties with a high specific capacitance of 890 C g-1 at 1 A g-1. It also demonstrates excellent cycle stability with an 83.5% capacitance retention rate after 5000 cycles at 10 A g-1. Importantly, when assembled into a asymmetric supercapacitor, it exhibits a high energy density (43.3 W h kg-1) and power density (800 W kg-1). The exceptional electrochemical capacity is attributed to the structural features, refined grains, and enhanced conductivity. The above results indicate that CNTs/NiCo2S4 composite electrode materials have great potential application in energy-storage devices.

In Situ Binder-Free and Hydrothermal Growth of Nanostructured NiCo2S4/Ni Electrodes for Solid-State Hybrid Supercapacitors

Herein, we report a comparison of the electrochemical performance of two kinds of NiCo2S4-based electrodes for solid-state hybrid supercapacitors (HSCs). For the binder-free electrode, NiCo2S4 was grown on Ni foam by the chemical bath deposition (CBD) method. For the binder-using electrode, NiCo2S4 powder was synthesized by the hydrothermal method. FESEM images depicted the hierarchical nanostructure of NiCo2S4 synthesized by the hydrothermal method and uniform distribution of nanostructured NiCo2S4 grown on Ni foam by the CBD method. Half-cell studies of both NiCo2S4 electrodes showed them exhibiting battery-type charge storage behavior. To assemble HSCs, NiCo2S4 and activated carbon were used as a positive and negative electrode, respectively. Electrochemical studies of the HSCs showed that the accessible potential window was wide, up to 2.6 V, through cyclic voltammetry (CV) analysis. Chronopotentiometry (CP) studies revealed that the energy and power densities of binder-using HSC were 51.24 Wh/kg and 13 kW/kg at 1 Ag−1, respectively, which were relatively higher than those of the binder-free HSC. The binder-free HSC showed 52% cyclic stability, relatively higher than that of the binder-using HSC. Both HSCs, with unique benefits and burdens on energy storage performance, are discussed in this work.

Plant polyphenols induced the synthesis of rich oxygen vacancies Co3O4/Co@N-doped carbon hollow nanomaterials for electrochemical energy storage and conversion

Reasonable hollow structure design and oxygen vacancy defects control play an important role in the optimization of electrochemical energy storage and electrocatalytic properties. Herein, a plant polyphenol tannic acid was used to etch Co-based zeolitic imidazolate framework (ZIF-67) followed by calcination to prepare a porous Co₃O₄@Co/NC hollow nanoparticles (Co₃O₄@Co/NC-HN) with rich oxygen vacancy defects. Owing to the metal-phenolic networks (MPNs), rich oxygen vacancy defects and the synergistic effect between Co₃O₄ and Co/NC, the box-like Co₃O₄@Co/NC-HN nanomaterials with large specific surface areas exhibit excellent supercapacitor performance and electrocatalytic activity. As expected, Co₃O₄@Co/NC-HN shows high specific capacity (273.9 mAh g^-1 at 1 A g^-1) and remarkable rate performance. Moreover, the assembled Hybrid supercapacitor (HSC, Co₃O₄@Co/NC-HN//Active carbon) device obtained a maximum energy density of 57.8 Wh kg^-1 (800 W kg^-1) and exhibited superior cycle stability of 92.6% after 4000 cycles. Notably, as an electrocatalyst, the nanocomposites exhibit small overpotential and Tafel slope. These results strongly demonstrate that both unique hollow structure and abundant oxygen vacancies designed from plant polyphenols provide superiorities for the synthesis of efficient and green multifunctional electrode materials for energy storage and conversion.

MOF-derived ZnCo2O4@NiCo2S4@PPy core-shell nanosheets on Ni foam for high-performance supercapacitors

The ZnCo₂O₄@NiCo₂S₄@PPy core-shell nanosheets material is prepared by directly growing leaf-like ZnCo₂O₄ nanosheets derived from the metal-organic framework (MOF) on Ni foam (NiF) via chemical bath deposition and annealing methods and then combining with NiCo₂S₄ and PPy via electrodeposition methods. The special core-shell structure formed by MOF-derived ZnCo₂O₄, NiCo₂S₄ and PPy creates a bi-interface, which could significantly promote the contact between electrode and electrolyte, provide more active sites and accelerate electron/ion transfer. And the combination of these three materials also produces a strong synergistic effect, which could further improve the capacitive performance of the electrode. Therefore, the ZnCo₂O₄@NiCo₂S₄@PPy/NiF electrode exhibits the maximum areal capacitance (3.75 F cm^-2) and specific capacitance (2507.0 F g^-1) at 1 mA cm^-2 and 0.5 A g^-1, respectively. Moreover, its capacitance retention rate is still 83.2% after 5000 cycles. In addition, a coin-type hybrid supercapacitor is assembled and displays a high energy density of 44.15 Wh kg^-1 and good cycling performance.

Sponge-like NiCo2S4 nanosheets supported on nickel foam as high-performance electrode materials for asymmetric supercapacitors

Herein, binder-free sponge-like NiCo₂S₄ nanosheets supported on Ni foam with ultra-high mass loading were synthesized via a facile one-step hydrothermal route.