Elsevier

Journal of Energy Storage

Volume 17, June 2018, Pages 318-326
Journal of Energy Storage

In-situ growth of MnO2 nanorods forest on carbon textile as efficient electrode material for supercapacitors

https://doi.org/10.1016/j.est.2018.03.015Get rights and content

Highlights

  • MnO2 nanorods forest is directly grown on highly conductive carbon textile with high surface area.

  • The self-supported electrode shows excellent supercapacitive (961 Fg−1) performance in an aqueous Na2SO4 electrolyte.

  • MnO2-NRF electrode exhibits good cycling stability by retaining 92% of its initial capacitance after 5000 cycles.

  • MnO2-NRF shows excellent adhesion with carbon textile substrate even after long term running.

Abstract

Nowadays, the design and fabrication of high-performance and low-cost electrode materials for energy storage and conversion systems are highly desired. The nanostructured materials are interesting for energy-related applications due to the large surface area, enormous active sites which ensure the complete utilization of active material. In this paper, we report a three-dimensional (3D) MnO2 nanorod forest network on carbon textile (MnO2–NRF@CT) with the hierarchical porous structure as a binder-free electrode material for supercapacitor. MnO2–NRF is directly grown on carbon textile surface by a simple one-step hydrothermal method. The carbon textile greatly improved the graphitization degree in MnO2–NRF composite. Typically, MnO2–NRF@CT sample indicates a partially graphitic structure having a low-intensity ratio of Raman D to G band (ID/IG = 0.68), which significantly increases the electrical conductivity and enhanced the performance of the supercapacitor. Consequently, the MnO2–NRF@CT porous architecture as supercapacitor electrode exhibits outstanding electrochemical performance (961 F g−1 at 1 mA cm−2 in 1 mol/L Na2SO4 electrolyte). The MnO2–NRF@CT shows good capacitance retention by achieving 92% of its initial capacitance after 5000 cycles. The long life and good stability highlighted its great potential for future supercapacitor applications.

Introduction

Energy is always an important issue for human beings. The ever-increasing population and economic development, raised the depletion of fossil fuels, resulting in massive emissions of greenhouse gases, climate changes, which create environmental problems [[1], [2]]. These facts inspired the researcher for the development of new technological aspects of clean and sustainable energy sources. Solar, wind and water splitting are the novel types of power sources having low exhaust emissions, and promising candidates for stationary and transportation uses [[3], [4]]. But unfortunately, these energy systems are often constrained by time and environmental conditions (e.g., the wind and solar) or geography (e.g., water). Therefore, energy storage systems, like supercapacitors (SCs) also known as electrochemical capacitors and batteries are needed to ensure continuous and balance power supply [5]. SCs have received intensive research attention from last decade owing to high power density and rapid charging/discharging process and can fulfil the gap between fuel cells and rechargeable batteries [[6], [7]]. SCs typically shows superior power density, safe operation and lifecycle. These favorable characteristics are beneficial for practical applications of supercapacitors in the future. However, their energy density needs to improve to compete the batteries. Currently, SCs energy densities are lower than that of conventional batteries [[8], [9]], therefore the enhancement of its energy density is a challenging task. Recently flexible energy storage devices attract great research attention due to the incorporation of foldable electronic equipment’s, e.g., mobile phones, displays, computers, etc. [[10], [11]]. Flexible solid-state SCs are particularly promising for achieving a compact, lightweight and reliable energy storage applications [[12], [13]]. The electrode material is the fundamental component of SCs and mostly dictates its ultimate performance [14]. Numerous kinds of substrates have been employed as a current collector to rouse the electrochemical properties of supercapacitors such as graphene [15], nickel foam [16], carbon papers and carbon textiles. Among them, CT is regarded as the best choice due to its flexibility, soft and excellent mechanical strength for direct growth of a positive material on it [17]. Usually, the active materials are coated or deposited on CT substrates and then used as an electrode for supercapacitor, which comprises of polymer-binders and conductive agent mixed with positive materials [[18], [19]]. In such situation, a part of electroactive sites of the positive material cannot contact with electrolyte due to use of conductive agents and binders. Therefore, the polymer-binder will decrease the inner diffusion of electrolyte ions into the electrode material and limits the supercapacitors performance. It is important to fabricate rational designs of electrodes for supercapacitor. Recently, directly grown nanostructured materials on conducting substrates without any binder, known as binder-free electrodes become an attractive technique among researchers [20]. Directly grown nanomaterials have some unique benefits, such as better electronic conductivity and more electroactive sites. Therefore, CT is chosen for the direct growth of active material for the fabrication of flexible electrodes of SCs [21].

Carbon, conducting polymers, transition metal oxides (TMOs) and transition metal dichalcogenides (TMCs) for Faradic redox supercapacitors show substantially higher specific capacitance as compared to carbon-based supercapacitors [22]. TMOs and conducting polymers are classically employed as electroactive positive materials for pseudocapacitors [[15], [23]]. One successful model is the application of RuO2 in the armed field due to its high specific capacitance of >600 F/g. However, toxicity issues and the higher cost of RuO2 limit its common application [24]. Therefore, incredible efforts have been made to develop inexpensive and environment-friendly alternatives, such as MnO2, Fe3O4, Co3O4, NiO [[25], [26], [27], [28]].

MnO2 is considered as an alternative electrode material for pseudocapacitors and widely studied owing to its high specific capacitance in aqueous electrolytes, and offer many technological features such as natural abundance, low cost, environmental friendliness and wide potential window [[29], [30]]. As with other electroactive transition metal oxides, manganese oxide stores electrical charge by simultaneous injection of electrons and charge-compensating cations into the solid and are, therefore, potentially useful for charge storage applications such as cathodes in secondary lithium batteries, electrochromic devices, and recently electrochemical supercapacitors in aqueous electrolytes [31]. Charge storage properties of transition metal oxides are closely related to electrical conductivity in the solid phase and ionic transport within the pores. In this regard, layered manganese oxides possessing bicontinuous networks of solid and pore are attractive candidates for application as active electrode materials [32]. However, the low electrical conductivity of MnO2 hinders its practical applications. MnO2–based electrodes materials reported in the literature are mostly in powder form and thus need binders and conductive agents for the fabrication of electrodes, which limits their performance up to few thousand cycles [33], therefore we emphasized to enhance the conductivity by directly growing it on highly conductive carbon textile substrate [24].

In this study, we purposed in-situ 3D MnO2 nanorod forest network on carbon textile (MnO2–NRF@CT) with the hierarchical porous structure as a binder-free electrode material for supercapacitor. CT substrate shows good performance for relatively high mass loading of MnO2 without any mechanical peeling or pressing process. The MnO2 shows a strong binding with carbon textile substrates, which is useful for stable cycling performance. The as-prepared electrode exhibits an outstanding specific capacitance of 961 F g−1 at a current density of 1 mA cm−2 and 92% capacitance retention after 5000 charge/discharge cycles in 1 mol/L sodium sulphate (Na2SO4) neutral aqueous electrolyte, which could be possibly useful for upcoming large-scale stationary energy storage applications.

Section snippets

Chemicals and materials

Flexible carbon textile with a thickness of 0.20 mm was purchased from Shanghai LCMT (Lishuo Composite Material Technology) Company. Potassium permanganate (KMnO4), sodium hydroxide (NaOH), and nitric acid (HNO3) were purchased from Beijing Sinopharm Chemical Reagent Co., Ltd., China. All the chemicals in this article were of analytical grade.

Hydrothermal synthesis of MnO2–NRF @ CT

Carbon textile (CT) was employed as a substrate and α-MnO2 nanorods forest was grown on CT by the simple hydrothermal method. CT was soaked into a

Structure characterization

The XRD pattern of as-prepared MnO2–NRF@CT is illustrated in Fig. 2(a). The diffraction peaks are assigned to the standard α–MnO2 phase and the position and intensity of the peaks coincide with the standard card (JCPDS No. 44-0141) [34], while the residual broad peak at 2 θ around 25° came from the carbon textile. The sharp diffraction peaks indicate the highly crystalline nature of the as-prepared samples. The powder α–MnO2 XRD pattern has been provided in Fig. 2(a) for comparison. Fig. 2(b)

Conclusions

In-situ 3D MnO2 nanorod forest was rationally grown on flexible carbon textile via a simple facile hydrothermal route. The MnO2–NRF on CT is directly used for the high-performance supercapacitors binder-free electrode. The electrochemical measurements demonstrate a maximum specific capacitance of 961 F g−1 at a current density of 1.0 mA cm−2, showing a good cycling stability with 92% retention of the specific capacitance after 5000 GCD cycles. The advantages of such pseudocapacitor electrode

Acknowledgements

The authors acknowledge funding support from the National Natural Science Foundation of China (Grant No. 61373072), National Key Scientific Instruments and Equipment Development Special Fund (2011YQ14014506 and 2011YQ14014507) and University of Science and Technology Beijing (fundamental development and Chinese Government Scholarship program).

References (56)

  • J. Cao et al.

    Materials and fabrication of electrode scaffolds for deposition of MnO2 and their true performance in supercapacitors

    J. Power Sources

    (2015)
  • A. Sadezky

    Raman microspectroscopy of soot and related carbonaceous materials: spectral analysis and structural information

    Carbon N. Y.

    (2005)
  • Y. Jiang et al.

    Flexible of multiwalled carbon nanotubes/manganese dioxide nanoflake textiles for high-performance electrochemical capacitors

    Electrochim. Acta

    (2015)
  • M. Tian et al.

    Conductive reduced graphene oxide/MnO2 carbonized cotton fabrics with enhanced electro -chemical, -heating, and -mechanical properties

    J. Power Sources

    (2016)
  • Shuijian He et al.

    Application of biomass-derived flexible carbon cloth coated with MnO2 supercapacitor

    J. Power Sources

    (2015)
  • M.S. Javed et al.

    High performance solid state flexible supercapacitor based on molybdenum sulfide hierarchical nanospheres

    J. Power Sources

    (2015)
  • N. Li et al.

    Controllable synthesis of different microstructured MnO2 by a facile hydrothermal method for supercapacitors

    J. Alloys Compd.

    (2017)
  • X. Su et al.

    High-performance α-MnO2 nanowire electrode for supercapacitors

    Appl. Energy

    (2015)
  • M. Armand et al.

    Building better batteries

    Nature

    (2008)
  • T. Chen et al.

    Flexible supercapacitors based on carbon nanomaterials

    J. Mater. Chem. A

    (2014)
  • B. Li et al.

    Ultrathin nickel–cobalt phosphate 2D nanosheets for electrochemical energy storage under aqueous/solid-state electrolyte

    Adv. Funct. Mater.

    (2017)
  • M. Huang et al.

    Merging of Kirkendall growth and Ostwald ripening: CuO@MnO2 core-shell architectures for asymmetric supercapacitors

    Sci. Rep.

    (2014)
  • P. Simon et al.

    Materials for electrochemical capacitors

    Nat. Mater.

    (2008)
  • X. Li et al.

    Facile synthesis and shape evolution of well-defined phosphotungstic acid potassium nanocrystals as a highly efficient visible-light-driven photocatalyst

    Nanoscale

    (2017)
  • Y. Xu et al.

    Holey graphene frameworks for highly efficient capacitive energy storage

    Nat. Commun.

    (2014)
  • M.S. Javed et al.

    Flexible full-solid state supercapacitors based on zinc sulfide spheres growing on carbon textile with superior charge storage

    J. Mater. Chem. A

    (2016)
  • G.A. Ferrero et al.

    Free-standing hybrid films based on graphene and porous carbon particles for flexible supercapacitors

    Sustain. Energy Fuels

    (2017)
  • L. Zhang et al.

    Fabrication of metal molybdate micro/nanomaterials for electrochemical energy storage

    Small

    (2017)
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