Elsevier

Materials Letters

Volume 264, 1 April 2020, 127358
Materials Letters

Self-assembled three-dimension flower-like nickel hydroxide synthesis with one-pot hydrothermal method for electrochemical applications

https://doi.org/10.1016/j.matlet.2020.127358Get rights and content

Highlights

  • It is found that the (NH4)6Mo7O24·4H2O has a great effect on the morphology and phase of nickel hydroxide.

  • Self-assembled flower-like nickel hydroxide were obtained by an easy hydrothermal method.

  • The composites of α-Ni(OH)2 and β-Ni(OH)2 show high specific capacitance (1111.3 F g−1 at 1 A g−1).

  • The composites of α-Ni(OH)2 and β-Ni(OH)2 show a great multiplier performance (720 F g−1at 20 A g−1).

Abstract

Self-assembled flower-like nickel hydroxide was obtained by adding a small amount of (NH4)6Mo7O24·4H2O (NMH) in the hydrothermal process. The research mainly focuses on the influence of NMH on the structure and phase composition of nickel hydroxide. As the electrode material of supercapacitor, the electrochemical performance of the products obtained by adding NMH is significantly improved, showing higher specific capacitance and better cycling performance. The specific surface area and electrochemical properties of conducts reach the 218.66 m2 g−1 and 1111.3 F g−1 at 1 A g−1, respectively. The prepared samples also show excellent cycle performance (after1000 cycles, 90.4% capacitance retention) and prominent multiplier performance (720 F g−1 at 20 A g−1).

Introduction

With the rapid development of science and technology, the demand for fossil energy is increased rapidly. However, since fossil energy is limited and non-renewable, it is urgent to seek clean, efficient and sustainable energy [1]. Due to many advantages of high specific capacitance, high power density and reliable cycle stability, supercapacitor is regarded as an energy storage equipment with great application value [2], [3]. In recent years, transition metal hydroxides and oxides have been extensively researched because of the excellent redox properties and ultrahigh theoretical specific capacitance [4].

Nickel hydroxide, a typical transition metal hydroxide, is of great interest due to its high theoretical specific capacitance, low cost and unique electrochemical redox activity [5]. However, its inherent inferior conductivity and bulk useless volume limit its application in the field of energy storage. It’s well known that the conductivity improvement and structural design to the materials are the two main methods to improve the properties of the hosts. Zhang et al. reported Ni(OH)2/graphene composite synthesized by refluxing method and demonstrated specific capacitance from 1064 F g−1 to 1503 F g−1 at 2 mV s−1 [6]. Other more, the highly specific surface area and high porous structure, faster and easy electrolyte diffusion at active sites, can enhance electrochemical properties [7]. Lokhande et al. demonstrated a flower-like β-Ni(OH)2 nanostructure synthesized by simple chemical bath deposition which the maximum specific capacitance was found 1065 F g−1 at 15 mA s−1 [8]. self-assembled pompon-like Ni(OH)2 microspheres with hollow interiors were obtained by a simple hydrothermal method and they had excellent capacitance behavior of 1028.5 F g−1 at a charge/discharge current density of 2.22 A g−1 [9].

It is well known that higher specific surface and larger distance between the layer can highly improve the electrochemical performance. Herein, flower-like Ni(OH)2 (α and β phase) is obtained through adding NMH to control the morphology and phase of the material in the hydrothermal process. The max specific capacitance and specific surface area of samples are measured to be 1111.3 F g−1 at 1 A g−1 and 218.7 m2 g−1, respectively, which are much more than the sample without addition of NMH.

Section snippets

Experimental section

All chemicals are analytical pure and without further purification. First, Ni(AC)2·4H2O and a certain amount of NMH are dissolved in 60 ml of deionized water with continuous stirring. Second, The pH range of mixed solution is adjusted to 9 with a certain amount of ammonium hydroxide. Then, the resulting solution is transferred to a 100 ml Teflon reactor at 160 ℃ for 12 h. After cooling to room temperature, repeated centrifugation with anhydrous ethanol and deionized water is utilized to obtained

Results and discussion

Fig. 1 shows the XRD patterns of the pure-Ni(OH)2 (no NMH) and m-Ni(OH)2 (adding certain amount of NMH). It can be seen from Fig. 1a that the sharp diffraction peaks at 19.2, 33.0, 38.5, 52.0, 58.9 and 62.6° are obviously observed, which correspond to the (0 0 1), (1 0 0), (1 0 1), (0 1 2), (1 1 0) and (1 1 1) diffraction planes of β-Ni(OH)2 (PDF No. 74–2075), respectively. The high and sharp (0 0 1) peak at 19.24° indicates well-crystallinity and Ni(OH)2 layers along c axis direction. In Fig. 1

Conclusion

In summary, a facile hydrothermal method has been proposed to synthesize the self-assembled flower-like Ni(OH)2. It is found that the NMH has a great effect on the morphology and phase of nickel hydroxide in hydrothermal synthesis. The max specific capacitance of flower-like Ni(OH)2 is 1111.3 F g−1 at 1 A g−1 and a great capacity retention of 64.8% (720 F g−1 at 20 A g−1). Furthermore, it shows prominent cycle performance, that is, 90.4% after 1000 cycle at 20 A g−1. The results demonstrate that NMH do

CRediT authorship contribution statement

The first author, Yuansheng Wu, mainly undertook the paper's Writing - original draft.

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

The authors gratefully thank the financial supports of Nation Natural Science Foundation of China (Grant No. 51762033) and Natural Science Foundation of Jiangxi Province (20181BAB206009).

References (9)

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    The samples' morphology was displayed in Fig. 7. Unlike the hierarchical self-assembly mechanism [16,30–32] of the flower-like architecture's formation, an self-shrink mechanism was proposed by analyzing the SEM images in different reaction time. First, nickel-organic composite (mainly consisted of formate and alkoxide) was generated and assemble to hollow spheres in ethylene glycol solution as Fig. 7(a).

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