Elsevier

Advanced Powder Technology

Volume 30, Issue 12, December 2019, Pages 3118-3126
Advanced Powder Technology

Original Research Paper
A facile preparation of graphene/reduced graphene oxide/Ni(OH)2 two dimension nanocomposites for high performance supercapacitors

https://doi.org/10.1016/j.apt.2019.09.019Get rights and content

Highlights

Abstract

A Ni(OH)2 composite with good electrochemical performances was prepared by a facile method. Ni(OH)2 was homogeneously grown on the hydrophilic graphene/graphene oxide (G/GO) nanosheets, which can be prepared in large scale in my lab. Then G/GO/Ni(OH)2 was reduced by L-Ascorbic acid to obtain G/RGO/Ni(OH)2. Caused by the synergy effects among the components, the G/RGO/Ni(OH)2 electrode showed good electrochemical properties. The G/RGO/Ni(OH)2 electrode possessed a specific capacitance as high as 1510 F g−1 at 2 A g−1 and even 890 F g−1 at 40 A g−1. An asymmetric supercapacitor device consisting of G/RGO/Ni(OH)2 and reduced graphene oxide (RGO) was installed and displayed a high energy density of 44.9 W h kg−1 at the power energy density of 400.1 W kg−1. It was verified that the G/GO nanosheets are ideal supporting material in supercapacitor.

Introduction

Over the past decade, with the rapid consumption of fossil fuel and the increasingly serious environmental pollution, there has been a strong desire to explore new energy storage equipment [1], [2], [3]. Among available equipment of storing energy, supercapacitors have attracted wide attentions due to their excellent features [4], [5], [6]. Usually supercapacitors are divided into three categories: electrical double layer capacitors (EDLCs), pseudocapacitors, and hybrid capacitors. EDLCs, depending on physical adsorption and desorption of ions, have a low specific capacitance [7]. Pseudocapacitors, relying on the faradaic reactions of electrodes, possess high energy density and poor cycling stability [8], [9]. To optimize the above two supercapacitor, researchers have designed hybrid supercapacitors combining EDLCs and pseudocapacitors [10]. Usually carbon materials (graphene, carbon nanofibers) are employed as electrode materials for EDLCs. Metal oxides or metal hydroxides (for MnO2, Ni(OH)2) and conducting polymers (such as polyaniline) are used as an electrode material for pseudocapacitors. Compared with EDLCs, pseudocapacitors possess ideal capacity.

In recent years, transition-metal oxide or hydroxides materials for pseudocapacitor have attracted attentions of academia due to high theoretical capacity. In all of them, Ni(OH)2 stands out for its low cost and excellent theoretical capacity. In reported articles, low conductivity, low power performance and poor cycling stability limit practical applications of Ni(OH)2 [11], [12], [13]. Graphene, with remarkable characteristics (such as high electrical conductivity), has attracted worldwide attention since its advent. A lot of experiments show that graphene or graphene oxide is an ideal supporting matrix for active materials [14], [15], [16]. In situ reaction of nickel salts in graphene or graphene oxide suspension is a common synthetic route to prepare graphene/Ni(OH)2 composite. Wang [17] reported that Ni(OH)2 nanocrystals grown on graphene sheets by hydrothermal reaction at 180 °C for 10 h, which possessed a high specific capacitance. In this process, hydrophobic graphene was dispersed in organic solvent DMF which was toxic and environmentally unfriendly. And the time consumed by this process was long. Lee [18] used non-aqueous method to synthesize rGO/α-Ni(OH)2, which presented excellent electrochemical properties. Li [19] reported a green method to reduce graphene oxide with Ni powder and obtained Ni(OH)2/RGO composite. Graphene oxide, with rich oxygen-containing functional groups, is easy to couple with Ni(OH)2. However, reduced graphene oxide still remains high resistance, which is not best for energy storage applications. It is speculated that the uniform combination of graphene with high electrical conductivity and graphene oxide with rich oxygen-containing functional groups may improve the electrochemical properties of composites. However, it is difficult to obtain uniform composite nanosheets of graphene with high hydrophobicity and graphene oxide in green aqueous solution by simple mechanical mixing.

In this paper, G/GO nanosheets prepared by liquid-shear-exfoliation using graphite oxide as an additive in our lab [20], [21] were employed as a supporting substrate and Ni(OH)2 grew on G/GO nanosheets to obtain G/RGO/Ni(OH)2 composite. G/GO could be directly dispersed in aqueous solution without organic solvent, and the introduction of graphene increased the conductivity of G/GO. The G/RGO/Ni(OH)2 exhibited a high specific capacitance and good cycling stability, which were superior to the RGO/Ni(OH)2 from pure graphene oxide. Finally, the asymmetric G/RGO/Ni(OH)2//RGO supercapacitor device was assembled, showing good electrochemical properties. Those results indicate that G/GO is suitable for the preparation of composite materials for energy storage devices.

Section snippets

Materials

Graphite powder was bought from Fuchen Chemicals Reagents Company (Tianjin, China) and high purity graphite was derived from Qingdao. Nickel sulfate (NiSO4·6H2O), L-Ascorbic acid (L-AC) and ammonia (NH3·H2O, 35 wt%) were obtained from Beijing Chemical Works. Nickel foam with a thickness of 1.0 mm was bought by Kunsan Teng Er Hui Technology Co., Ltd.

Synthesis of materials

Preparation process of G/GO were described in the supporting information. The 100 mL G/GO dispersion was obtained by adding G/GO powder (0.1 g) into

Results and discussion

In order to determine the optimum mass ratio, SEM and simple electrochemical properties of G/RGO/Ni(OH)2 (3:1, 5:1, 8:1) were tested. Compared with G/RGO/Ni(OH)2 (8:1), the Ni(OH)2 nanosheets on G/RGO (5:1) grow more uniformly (Fig. 2). Moreover, the existence of Ni(OH)2 will prevent restacking of G/RGO sheets to avoid the loss of a large amount of active sites. When the mass ratio of NiSO4·6H2O to G/GO is more than 5, the accumulation of Ni(OH)2 leads to the decrease of the surface area of the

Conclusion

G/RGO/Ni(OH)2 composite as a promising material for supercapaitor with good electrochemical properties was prepared by a facile method. G/GO, which was low cost, green, and easy to be scaled up, was as a supporting matrix. Due to the lightly oxidized and electrically conducting graphene sheets, G/GO nanosheets prepared by our lab were benefit to the growth of large size Ni(OH)2. And the introduction of graphene in G/GO increased the electrical conductivity of composite, which would accelerate

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 21676023).

References (40)

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