Abstract:To meet the demand of high‐performance electrode materials for supercapacitors, it is highly desirable to design and develop a new class of electrode materials with superior electrochemical performance. Here, we used a simple hydrothermal method to synthesize NiCo2S4‐anchored graphene nanosheets (NiCo2S4/GNS) for high‐performance supercapacitors. Benefiting from the synergistic effect of graphene and NiCo2S4, the as‐prepared composite exhibits outstanding electrochemical performances, such as high specific cap… Show more
“…2, it can be concluded that Ni 2+ , Co 2+ , Ni 3+ , Co 3+ and S 2− are present in the NiCo 2 S 4 thin films. The XPS results closely agree with previously reported data for NiCo 2 S 4 thin films 30,34 .Figure 2( a ) Survey spectrum of the optimized NiCo 2 S 4 sample, ( b , c ) Core level spectra for Ni 2p, Co 2p, and S 2p, respectively, at optimized sample NCS:25 thin film on Ni mesh.…”
Here, we developed a new approach to synthesize NiCo2S4 thin films for supercapacitor application using the successive ionic layer adsorption and reaction (SILAR) method on Ni mesh with different molar ratios of Ni and Co precursors. The five different NiCo2S4 electrodes affect the electrochemical performance of the supercapacitor. The NiCo2S4 thin films demonstrate superior supercapacitance performance with a significantly higher specific capacitance of 1427 F g−1 at a scan rate of 20 mV s−1. These results indicate that ternary NiCo2S4 thin films are more effective electrodes compared to binary metal oxides and metal sulfides.
“…2, it can be concluded that Ni 2+ , Co 2+ , Ni 3+ , Co 3+ and S 2− are present in the NiCo 2 S 4 thin films. The XPS results closely agree with previously reported data for NiCo 2 S 4 thin films 30,34 .Figure 2( a ) Survey spectrum of the optimized NiCo 2 S 4 sample, ( b , c ) Core level spectra for Ni 2p, Co 2p, and S 2p, respectively, at optimized sample NCS:25 thin film on Ni mesh.…”
Here, we developed a new approach to synthesize NiCo2S4 thin films for supercapacitor application using the successive ionic layer adsorption and reaction (SILAR) method on Ni mesh with different molar ratios of Ni and Co precursors. The five different NiCo2S4 electrodes affect the electrochemical performance of the supercapacitor. The NiCo2S4 thin films demonstrate superior supercapacitance performance with a significantly higher specific capacitance of 1427 F g−1 at a scan rate of 20 mV s−1. These results indicate that ternary NiCo2S4 thin films are more effective electrodes compared to binary metal oxides and metal sulfides.
“…Few layers structure of graphene formed by the two reduction methods are evident in their atomic force microscopy images and the corresponding line profiles, Figures 1a and 1b, indicating that each flake approximately contains 3-4 graphene layers.The Raman spectra demonstrate a higher I D /I G ratio (intensity of defect band/intensity of graphitic band) for the FLG formed by borohydride reduction method compared to the corresponding FLG obtained by Fe powder reduction method, ( Figure S1), suggesting the presence of more hydrophilic functionalities in the former. [37,38] This is further clear from the Xray photoelectron spectra (XPS), Figure 1c, where carbon attached to oxygen functionalities are evidently present in FLG obtained by borohydride reduction method. Such signals are negligible in the case of FLG obtained by Fe powder reduction method.…”
We report a rechargeable sodium-ion battery in an aqueous environment with hydrophobic few-layer graphene as the capacitive anode and hexacyanometallate as the insertion cathode. Owing to the lack of hydrophilic functionalities, sodium-ion adsorption is selectively favored over H + adsorption at the hydrophobic anode/electrolyte interface without the complexity of widely encountered hydrogen-ion insertion/H 2 evolution. Hydrophobicity precludes chemical bond formation with sodium ions, thereby improving reversibility and extended cyclability during charge discharge chemistry.In the context of the geographic and temporal variations of renewable energy resources, metal ion batteries and new generation supercapacitors assume larger space as efficient energy storage modules. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] So far non-aqueous metal ion batteries have dominated the consumer electronics, transport technologies and electrical grid as the prime storage technology. [17][18][19] Aqueous metal ion batteries though being environmentally benign, are rare in these contexts mainly due to serious instability of the state of the art anode materials in aquatic environment. [20][21][22] They suffer from spontaneous deinsertion reactions, unwanted swelling, undesirable proton insertion and parasitic H 2 evolution reactions, consequently degrading the anode entity during the long run. [23][24][25][26] The seminal works of Goodenough et. al., Wainwright et al, Yi Cui et. al, and Kang Kisuk et al., on anode materials for aqueous metal ion batteries are noteworthy in this direction. [23,[27][28][29][30][31][32][33] Here we report an aqueous sodium ion battery with extended cyclability using hydrophobic few layer graphene (FLG) as sodium ion adsorption anode and metal hexacyanoferrate (MHF) as the insertion cathode in aquatic environment. Hydrophobic FLG was produced by the reduction of graphene oxide's (GO) hydrophilic functionalities using Fe powder over conventionally used chemical reducing agents such as hydrazine and NaBH 4 [34,35] which predominantly yielded incompletely reduced GO thereby affecting its electrical and electronic properties. [34][35][36] We show here that the mode of reduction and therefore the hydrophobicity of FLG noticeably affect metal ion adsorption and charge-discharge chemistry at the anode/ electrolyte interface.FLG formed by two types of reduction processes are compared here, one by the Fe powder reduction method and the other by the conventional borohydride reduction method (see experimental section for more details). Few layers structure of graphene formed by the two reduction methods are evident in their atomic force microscopy images and the corresponding line profiles, Figures 1a and 1b, indicating that each flake approximately contains 3-4 graphene layers.The Raman spectra demonstrate a higher I D /I G ratio (intensity of defect band/intensity of graphitic band) for the FLG formed by borohydride reduction method compared to the corresponding FLG obtained by Fe powder reduction m...
“…To further evaluate NiCo 2 O 4 /MnO 2 core/shell composites electrode for real application, a series of asymmetric supercapacitor devices are assembled by using NiCo 2 O 4 /MnO 2 core/shell composites electrode as the cathode and biochar as the anode in 6 M KOH electrolyte with one piece of PTFE film as the separator . Three types of biochar (pomelo peel (PPC), banana peel (BPC) and buckwheat hull (BHC)) are processed (schematic ).…”
In this work, three dimensional (3D) hierarchical structure electrode of MnO2 nanosheets decorated on needle‐like NiCo2O4 nanocones hybrid arrays on Ni foam is designed by a two‐step hydrothermal process. In this special structure, 3D hierarchical NiCo2O4/MnO2 core/shell composites have high specific surface area and large pore structure, which makes it easier to reach the active site, and shorten the ion transport path. Used as electrode for supercapacitors, the composites can develop their respective strengths, and the synergies between different components can also improve capacitance and speed capacity. The electrochemical results exhibit that the NiCo2O4/MnO2 core/shell electrodes display a large capacitance of 816 F⋅g−1 at the current density of 5 mA⋅cm−2, and show an excellent cycling stability (81% retention after 5000 cycles). Four Asymmetric supercapacitors (NiCo2O4/MnO2//BPC (banana peel), NiCo2O4/MnO2//BHC (buckwheat husk), NiCo2O4/MnO2//PPC (pomelo peel), and NiCo2O4/MnO2//AC (activated carbon)) using the NiCo2O4/MnO2 core/shell as a positive electrode and biochar as a negative electrode are assembled. The results indicate that all the asymmetric supercapacitors deliver a high operation voltage of 1.6 V, and NiCo2O4/MnO2//BPC exhibits excellent specific capacitance (85.4 F⋅g−1 at the current density of 5 mA⋅cm−2), high energy density (30.4 Wh⋅kg−1 at the power density of 133.5 W⋅kg−1) and remarkable cycling stability (only decrease by 12% after 5000 cycles).
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