Elsevier

Synthetic Metals

Volume 275, May 2021, 116751
Synthetic Metals

Hierarchical porous CoFe2O4/CoFe2Se4 nanosheet as supercapacitor electrodes: Effect of selenium content and pore structure on electrochemical performance

https://doi.org/10.1016/j.synthmet.2021.116751Get rights and content

Highlights

  • CoFe2O4 porous nanosheet was controllably prepared by solvent ratio and structure-directing agent.

  • Sodium selenite was used as selenizing agent to directly selenize CoFe2O4 porous nanosheet.

  • CoFe2O4/CoFe2Se4 has excellent specific capacitance of 933.6 F g−1 at 1 A g−1.

Abstract

Improving electrode conductivity and increasing electrode specific surface area are two strategies to enhance the storage performance of supercapacitors. Generally, to improve the conductivity of the electrode, a conductive polymer is usually coated on electrode. Nevertheless, polymer covers the pore structure, thus reduce the specific surface area of electrode material, which is not conducive to electrolyte contact and electron transfer. Therefore, the selenide nanosheet layer can be precipitated from the outer layer of CoFe2O4 nanosheet by means of selenation reaction, which can not only increase conductivity of electrode, but also increase the specific surface area of electrode, which can kill two things with one stone. So, the as-prepared CoFe2O4/CoFe2Se4 porous nanosheet electrode as the positive electrode shows an outstanding specific capacity of 933.6 C g−1 (1 A g−1). The device operating voltage of an aqueous asymmetric supercapacitor is 1.6 V, the energy density is 112.2 Wh kg−1 (power density of 400 W kg−1). The aqueous asymmetric supercapacitor has good cycle life, after 4000 cycles the capacity retention is 92.1%. Based on the discussion of charging time and charging current of mechanical energy charging supercapacitor, a satisfactory result is obtained, which is beneficial to the collection and utilization of mechanical energy in practical application.

Graphical Abstract

By controlling the pore structure of CoFe2O4 nanosheet, the CoFe2O4/CoFe2Se4 composites with different pore structure were obtained after selenization.

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Introduction

Mechanical energy generated by human activities, if it can be collected efficiently and utilized, may become a third type of sufficient green energy [1]. In addition, although mechanical energy can be used at any time, devices that collect and store mechanical energy need to be flexible and convenient, and have large power density and energy density. Therefore, supercapacitors stand out from many stockpile equipment and become one of the candidates of mechanical energy storage equipment. Because of its fast charging speed, high current tolerance, and power density, energy density and high capacity are also excellent [2]. According to energy storage mechanism, supercapacitors can be divided into two types: double-layer capacitor and pseudocapacitor [3]. The former is the charge stored on surface of electrode, while the latter is a reversible Faraday redox reaction on electrode [4]. It is observed that specific surface area and conductivity of electrode play a key role in the property of supercapacitors. Herein, improving conductivity and specific surface area of the electrode material can certainly improve electrochemical performance of the supercapacitor [5].

In the preliminary work of our research group, the conductivity and specific surface area properties of CoFe2Se4 are excellent [2]. It has been proved in other work that metal selenides have better conductivity and electrochemical properties than metal oxides. For example, Chandu et al. demonstrated CoFe2Se4 nanorods electrode for asymmetric supercapacitors (183.4 mAh g−1) [6]. Mohammadi et al. prepared GW-FeS2-FeSe2-CSS with specific capacity of 352.3 F g−1 [7]. Song et al. reported CoFe2O4/CoFe2Se4 nanobox electrode with 463.27 F g−1 [2]. Li et al. illustrated that NiCo2Se4 nanotubes have good specific capacity 461 F g−1 [8]. And Yu et al. reported NiSe nanosheets electrode with 443 mA h g−1 [9]. According to the above, the synergies between selenides and other materials can improve the performance of supercapacitors. Moreover, binary metal oxides are often used as the positive pole of supercapacitors. Because of its multistage oxidation state, the property of the binary metal oxides are better than that of the single metal oxides, for instance NiFe2O4 [10], MnFe2O4 [11], and CoFe2O4 [12]. Among of them, spinel CoFe2O4 electrodes have outstanding electrochemical performances and low cost. The direct selenization of CoFe2O4 into a composite of selenide and oxide by sodium selenite can not only improve the conductivity of CoFe2O4, but also increase the specific surface area [13].

In general, we prepared various CoFe2O4 nanosheet on NF by a simple method for controlling solvent ratio and structural inducer. The nanosheet of CoFe2O4 can be adjusted easily by changing ratio of several solvents and combination of structural inducer. In addition, CoFe2O4 is directly formed a CoFe2O4/CoFe2Se4 core-shell structure composite by selenation. (i) CoFe2O4/CoFe2Se4 not only improves conductivity of electrode, but also increases the specific surface area of composite electrode;(ii) the controllable preparation of CoFe2O4 nanosheet offers the possibility of multiple composite structures for the composite electrode. Benefiting from these advantages, the CoFe2O4/CoFe2Se4 electrode has a specific capacity of 933.6 C g−1 at 1 A g−1 in 3 M KOH electrolyte. The CoFe2Se4 and CoFe2O4 composites with different selenium content and pore structure can be prepared in a controllable manner, providing guidance for the preparation of porous selenide in the future.

Section snippets

Results and discussion

Fig. 1 exhibits synthesis process of CoFe2O4 porous nanosheet and CoFe2O4/CoFe2Se4 porous nanosheet by simple hydrothermal method, and the morphology and structure of CoFe2O4 are controlled by structural inducer and solvent ratio. First, the suitable solvent is selected and the ratio of solvent to water is adjusted to prepare CoFe2O4 porous nanosheet with different morphology. Secondly, choose the appropriate structural inducer, and use the combination of solvent and structural inducer to

Conclusion

In conclusion, we controllably design and synthesize CoFe2O4 porous nanosheets by solvent ratio and structural inducer. And the CoFe2O4/CoFe2Se4 composite material with different selenium content is obtained by selenization. The as-fabricated CoFe2O4/CoFe2Se4 electrode as the positive supercapacitor electrode displays high specific capacity of 933.6 C g−1 at 1 A g−1. The CoFe2O4/CoFe2Se4//CNTs achieved excellent specific capacity of 505 C g−1 at 1 A g−1 and the energy density is 112.2 Wh kg−1

Experimental Section

The experimental materials and the preparation process of the materials, detailed characterization and electrochemical test requirements and formulas are included in the Supporting information.

CRediT authorship contribution statement

Kun Song: Conceptualization, Methodology, Software, Investigation, Writing - original draft. Rui Yang: Validation, Formal analysis, Visualization. Xiaoshuang Chen: Resources, Writing - review & editing, Supervision, Data curation. Yongjie Zheng: Resources, Writing - review & editing, Supervision, Data curation. Guoli Chen: Resources, Writing - review & editing, Supervision, Data curation. Nan Zhao: Writing, Formal analysis, Visualization.

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.

Acknowledgements

This work is financially supported by the Natural Science Foundation of Heilongjiang Education department (YSTSXK201810), the National Natural Science Foundation of China (NSFC, no. 21905146).

References (46)

  • Q. Dou et al.

    CoO/CoFe2O4 core/shell nanoparticles assembled in carbon sheets as anode materials for lithium ion battery

    J. Alloy. Compd.

    (2019)
  • Z. Zhou et al.

    Electronic structure studies of the spinel CoFe2O4 by X-ray photoelectron spectroscopy

    Appl. Surf. Sci.

    (2008)
  • W. Li et al.

    Template synthesis of C@NiCo2O4 hollow microsphere as electrode material for supercapacitor

    J. Alloy. Compd.

    (2018)
  • X. Guo et al.

    Design and synthesis of CoFe2O4 quantum dots for high-performance supercapacitors

    J. Alloy. Compd.

    (2018)
  • X. Feng et al.

    CoFe2O4 coated carbon fiber paper fabricated via a spray pyrolysis method for trapping lithium polysulfide in Li-S batteries

    Appl. Surf. Sci.

    (2019)
  • Y. Yang et al.

    Synthesis of ultrafine CoNi2S4 nanowire on carbon cloth as an efficient positive electrode material for high-performance hybrid supercapacitors

    J. Alloy. Compd.

    (2020)
  • D. Guo et al.

    Freestanding hierarchical nickel molybdate@reduced graphene oxide@nickel aluminum layered double hydroxides nanoarrays assembled from well-aligned uniform nanosheets as binder-free electrode materials for high performance supercapacitors

    J. Colloid Interface Sci.

    (2019)
  • B. Ren et al.

    3D CoFe2O4 nanorod/flower-like MoS2 nanosheet heterojunctions as recyclable visible light-driven photocatalysts for the degradation of organic dyes

    Appl. Surf. Sci.

    (2018)
  • W. Liu et al.

    Hierarchical CuCo2O4 nanourchin supported by Ni foam with superior electrochemical performance

    J. Alloy. Compd.

    (2018)
  • Y. Cheng et al.

    Mn3O4 tetragonal bipyramid laden nitrogen doped and hierarchically porous carbon composite as positive electrode for high-performance asymmetric supercapacitor

    J. Power Sources

    (2020)
  • S. Venkateshalu et al.

    Ti3C2Tx MXene and vanadium nitride/Porous carbon as electrodes for asymmetric supercapacitors

    Electrochim. Acta

    (2020)
  • X. Hao et al.

    Electrospun Fe2MoC/C nanofibers as an efficient electrode material for high-performance supercapacitors

    J. Power Sources

    (2020)
  • N. Xin et al.

    In-situ construction of metal organic frameworks derived Co/Zn–S sandwiched graphene film as free-standing electrodes for ultra-high energy density supercapacitors

    J. Power Sources

    (2020)
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