Nanosheet-assembled 3D flower-like MoS2/NiCo(OH)2CO3 composite for enhanced supercapacitor performance

doi:10.1016/j.jallcom.2020.158144

Journal of Alloys and Compounds

Volume 864, 25 May 2021, 158144

https://doi.org/10.1016/j.jallcom.2020.158144 Get rights and content

Highlights

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3D flower-like structure of MoS₂/NiCo(OH)₂CO₃ composite is synthesized.
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The composite is assembled by NiCo(OH)₂CO₃ nanosheets with MoS₂ nanospheres.
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The composite exhibits a high specific capacitance and good cycling stability.
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The 1T phase MoS₂ and flower-like structure enhance the supercapacitance.

Abstract

3D flower-like MoS₂/NiCo(OH)₂CO₃ (MoS₂/NiCoHC) composites are synthesized by a hydrothermal method using MoS₂ nanospheres as precursors. The microstructure of the composite is characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The MoS₂ nanospheres are served as nucleating agent to trigger the formation of NiCoHC nanosheets, which self-assemble into 3D flower-like MoS₂/NiCoHC particles. The MoS₂/NiCoHC composites exhibit a high supercapacitive performance with a specific capacity of 583 C g⁻¹ (1296 F g⁻¹) at 1 A g ⁻¹ and a long-term cycling stability by retaining 94.3% after 2000 cycles in 2 M KOH. Moreover, the asymmetric supercapacitor of MoS₂/NiCoHC as the positive electrode and commercial active carbon as the negative electrode achieves a high power density of 375 W kg⁻¹ at 16.4 Wh kg⁻¹. The enhanced performance of the MoS₂/NiCoHC composite can be attributed to the larger surface area provided by 3D flower-like structure and the synergy of the two hybrids.

Graphical Abstract

Introduction

As a new type of energy storage device, supercapacitors have attracted much attention due to their rapid charging and discharging process, long cycle stability, high power density and safe operation [1], [2], [3]. Therefore, they have been widely used in power supplies, such as digital telecommunication systems, hybrid electric vehicles, and various micro devices [4], [5]. However, commercial supercapacitors typically have the problem of low energy density (5–8 Wh kg⁻¹), which limits application fields [6]. Therefore, much efforts are devoted to improving the energy density of supercapacitors by designing special structures with large surface area or using multiple composites [7], [8], [9].

Transition-metal oxides or hydroxides are ideal supercapacitive materials because they can provide various oxidation states for the redox process in supercapacitors [10], [11]. Among the oxide candidates, hydroxycarbonates of divalent metal ions, expressed by M₂(OH)₂CO₃ (M is Ni, Co, Cu, Zn, Mg ions or two of them), are widely used as an electrode materials due to the high theoretical capacity, good cycle stability and environmental friendliness [12]. Various crystal morphologies have been synthetized, such as cobalt carbonate hydroxide nanorods [13], nickel-cobalt carbonate hydroxide nanoarrays [14], and copper-cobalt carbonate hydroxide nanospheres [15]. Among them, the specific capacity have reached as high as 789 F g⁻¹ at 1 A g⁻¹. However, hydroxycarbonates are mostly semiconductor materials, and the conductivity is negligible, which limits the supercapacitive performance at high charge and discharge rates [16]. To solve this problem, transition metal sulfides, such as MoS₂ [17], WS₂ [18] and TaS₂ [19], are introduced into the carbonate hydroxide material to improve the conductivity. As a typical example, MoS₂ can effectively enhanced the electrical conductivity due to the small bandgap for the anion exchange [20]. For example, Hao et al. incorporated flower-like MoS₂ nanosheets into Ni(OH)₂ nanoplates by a single-mode microwave hydrothermal technique, where the specific capacitance increased from 467 F g⁻¹ to 516 F g⁻¹ at 2 A g⁻¹ [21]. Meanwhile, Liu et al. [22] produced a hierarchical MoS₂/Co₃S₄/Ni₃S₄ nanosheet-on-nanorod arrays, which could provide multi-compositions for rich redox reactions, and thereafter, exhibited a high areal capacity of 3.94 F cm⁻² at 5 mA cm ⁻². In order to enhance the supercapacitance, hybrid materials with 2D or 3D nanostructure should be designed to obtain large surface area, good conductivity and good interface combination [23], [24].

In this paper, we construct a 3D flower-like MoS₂/NiCo(OH)₂CO₃ (MoS₂/NiCoHC) hybrid, which is in-situ synthesized by MoS₂ nanospheres and NiCoHC nanosheets. The MoS₂/NiCoHC composite electrode exhibits a large specific capacity (583 C g⁻¹ or 1296 F g⁻¹ at 1 A g⁻¹) and a good cyclic stability (94.3% after 2000 cycles). Furthermore, the experimental results of the assembled asymmetric supercapacitor indicate that the MoS₂/NiCoHC electrode exhibits a high power density, and can be used as a potential supercapacitor material.

Section snippets

Materials

The chemical reagents of ammonium tetrathiomolybdate ((NH₄)₂MoS₄), N, N-dimethylformamide (DMF), hydrazine hydrate (N₂H₄·H₂O), ammonium fluoride (NH₄F), Nickel (II) acetate tetrahydrate, Cobalt (II) acetate tetrahydrate, urea (CO(NH₂)₂), and KOH were purchased from Aladdin Industrial Cooperation in analytical grade and used as-received without further purification. Nickel foam (NF, 99.8% purity) with an average pore size of 10 µm and of 1.5 mm thick was purchased from Tianyuan Lizhiyuan

Microstructure of primitive MoS₂ and NiCoHC

The SEM image shows that the as-prepared MoS₂ powders are spherical particles with sizes of 400–1000 nm and an average diameter of 600 nm, as given in Fig. 2a. The surface of MoS₂ nanosphere contains some rough protuberances, as shown in the magnification of Fig. 2b. The element mappings of the Mo and S are shown in Fig. 2c and d, where the Mo and S are uniformly distributed in the spherical particle. Fig. 2e is the XRD pattern of MoS₂ powders, where the peaks at 14.4°, 29.0° and 39.5°

Conclusions

MoS₂/NiCoHC composites are synthesized by hydrothermal method using MoS₂ nanospheres as precursors. The microstructure of the MoS₂/NiCoHC is characterized by 3D flower-like particles assembled by NiCoHC nanosheets and MoS₂ nanospheres. Compared with the pure MoS₂ and NiCoHC, the MoS₂/NiCoHC composites exhibit better supercapacitive performance with a specific capacity up to 583 C g ⁻¹ (1296 F g ⁻¹) at 1 A g ⁻¹ and a long-term cycling stability with 94.3% of initial specific capacity after 2000

CRediT authorship contribution statement

A.Y. Chen, H.H. Liu, and P. Qi carried out the specimen preparation and performance tests. X.F. Xie, M.T. Wang, X.Y. Wang conceived and designed the experiments. M.T. Wang and A.Y. Chen contributed to the data analysis and experimental design. A.Y. Chen, H.H. Liu, and P. Qi wrote the manuscript with contributions from the other authors. All authors commented on the final manuscript and conclusions of this work.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We thank the National Natural Science Foundation of China (grants 51771121 and 51572173) and the fund provided by Science and Technology Committee of Shanghai Municipality (20ZR1437500). Professor Wang gratefully acknowledges the financial supports from Innovation Program of Shanghai Municipal Education Commission (2019-01-07-00-07-E00015) and Program of Shanghai Academic/Technology Research Leader (19XD1422900).

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This paper designs and produces ternary NiCo₂Al_x-LDH grown directly on a novel porous hollow structure of nitrogen-doped carbon capsule (N-Cc) conducting matrix with a PANI coating layer. The carefully designed NiCo₂Al_x-LDH/N-Cc@PANI electrodes exhibit electrochemical properties that are highly prized for their energy storage utility: specifically, a gravimetric capacitance of 1630F/g, an energy density of 55.75 Wh kg⁻¹ at the power density of 750 W kg⁻¹, and cyclic stability that achieves capacitance retention of 93.1 % after 5000 uninterrupted charge–discharge cycles. It should be noted that the electrode's excellent storage performance benefitted from the use of Al, which was crucial in stabilizing the LDH structure. It should also be pointed out that the 3D interconnected porous structure composed of N-Cc provides a greater accessible surface area and shortens the ion/electron transport distance, whilst PANI ensuring the LDHs remain firmly in contact with the conductive substrate.
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Citation Excerpt :
Especially, when the Pd was enhanced to 8666.8 W kg−1, the device could still retain 20.4 Wh kg−1 (Fig. 11). The Ed value (28.1 Wh kg−1) was also superior to those of SnS2@CF SSC (SnS2@CF//SnS2@CF, 13.9 Wh kg−1 at 551.7 W kg−1) [34], Mn-doped SnS2-graphene aerogel SSC (M-SnS2-GA//M-SnS2-GA, 18.02 Wh kg−1 at 1550 W kg−1) [47], SnS2/graphene nanosheets SSC (SnS2/G nanosheets//SnS2/G nanosheets, 23.5 Wh kg−1 at 880 W kg−1) [39], flower-like MoS2/NiCo(OH)2CO3//AC (MoS2/NiCoHC//AC, 16.4 Wh kg−1 at 375 W kg−1) [48], and CuO/MoS2//biomass-derived activated carbon (CuO/MoS2//BAC, 26.66 Wh kg−1 at 1599.6 W kg−1) [49]. But the value was still inferior than those of SnS2 nanorods//rGO (32.8 Wh kg−1 at 450 W kg−1) [31], SnS2/rGO nanosheets//AC (29.06 Wh kg−1 at 747.3 W kg−1) [28], and PANI/SnS2@CNTs/CFs//PANI/SnS2@CNTs/CFs (38.7 Wh kg−1 at 1 kW kg−1) [36].
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¹: These authors contributed equally to this work and should be considered co-first authors.

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Nanosheet-assembled 3D flower-like MoS2/NiCo(OH)2CO3 composite for enhanced supercapacitor performance

Highlights

Abstract

Graphical Abstract

Introduction

Section snippets

Materials

Microstructure of primitive MoS2 and NiCoHC

Conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgments

Electrochim. Acta

Electrochim. Acta

J. Power Sources

Chem. Eng. J.

J. Power Sources

Chem. Eng. J.

J. Phys. Chem. Solids

Electrochim. Acta

Electrochim. Acta

J. Alloy. Compd.

J. Alloy. Compd.

Electrochim. Acta

Nano Energy

Nano Energy

J. Power Sources

Inorg. Chem. Commun.

Mater. Lett.

J. Power Sources

J. Alloy. Compd.

Appl. Surf. Sci.

Electrochim. Acta

J. Power Sources

Nanosheet-assembled 3D flower-like MoS₂/NiCo(OH)₂CO₃ composite for enhanced supercapacitor performance

Microstructure of primitive MoS₂ and NiCoHC