One-pot synthesis of graphene/SnO₂/PEDOT ternary electrode material for supercapacitors

Highlights

• Graphene/SnO₂/PEDOT composites were obtained via one-pot synthesis method.

• No obvious capacitance loss was found for the composite at 1 A g⁻¹ after 5000 cycles in 1 M H₂SO₄.

• The composites present the enhanced capacitance and energy density in both acidic and neutral electrolytes.

Abstract

A ternary electrode material, based on graphene, tin oxide (SnO₂) and poly(3,4-ethylene-dioxythiophene) (PEDOT) has been obtained via one–pot synthesis for supercapacitors. The resulting composite graphene/SnO₂/PEDOT (GE/SnO₂/PEDOT) shows excellent electrochemical stability in acidic electrolyte, and good electrochemical performance with enhanced capacitance and energy density in both acidic and neutral electrolytes, compared to their binary composites. A maximum specific capacitance of 184 F g⁻¹ in 1 M H₂SO₄ and 180 F g⁻¹ in 1 M Na₂SO₄ respectively was obtained. Its energy density reaches 22 Wh Kg⁻¹ at a power density of 238.3 W kg⁻¹, and 17.1 Wh kg⁻¹ at a high power density of 5803.3 W kg⁻¹ in H₂SO₄. While in Na₂SO₄, the energy density achieves 23.4 Wh Kg⁻¹ at a power density of 253 W kg⁻¹ and 10.2 Wh Kg⁻¹ at power density of 3684 W kg⁻¹, respectively. The specific capacitance can still be retained about 100% and 70% at 1 A g⁻¹ after 5000 cycles in 1 M H₂SO₄ and Na₂SO₄, respectively. The improved electrochemical property of GE/SnO₂/PEDOT as electrode materials is mainly ascribed to the well-designed ternary nanostructure of the functional components with enhanced synergistic effects.

Introduction

Supercapacitors, recognized as an important type of device for next generation energy storage, represent a candidate for portable electronics and automotive applications due to their high power density, fast charge-discharge process and long cycling stability [1]. Generally, the energy storage mechanism of supercapacitors can be classified into two categories: one is electrochemical double layer capacitance (EDLC), and the other is based on the fast and reversible Faradic reactions (pseudocapacitors). The later exhibits higher specific capacitance than the former [2], [3]. However, for meeting the requirements of hybrid electric vehicles and large industrial equipment, most attraction is mainly concentrated in improving the energy density of the electrode materials, meanwhile maintaining the high specific capacitance and long lifetime. So far, carbon materials, conducting polymers and transition metal oxides have been widely studied as supercapacitor electrode materials [4], [5].

Graphene, a monatomic-thick 2D single layer of carbon atoms, has emerged as a fascinating electrode material for EDLC due to its higher surface area and superior electrical conductivity, and attracted an explosive interest in recent years [6]. It can be prepared from the chemical reduction of graphene oxide. Unfortunately, the single-layered graphene is easily restacking due to the strong Van der waals force, leading to the low specific power and energy density which limits its application in high power density supercapacitors. Therefore, combining with other components is a valuable solution to widen the application of graphene. Zhang et al. [7] introduced a simple and efficient approach to produce three-dimensional graphene-based porous materials with ultrahigh specific surface area and bulk conductivity. The electrode materials possessed superior electrochemical performance (231 F g⁻¹) in ionic liquid. Ning et al. [8] produces nanomesh graphene sheets with excellent electrochemical properties (specific capacitance up to 255 F g⁻¹) by a template chemical vapor deposition (CVD) approach. The nanomeshes graphene preventing agglomeration of the graphene sheets have only one to two layers by using porous MgO layers with polygonal shapes as a template. However the novel method need prepare the porous MgO layers by boiling treatment and high temperature calcinations. Therefore, the combination of graphene with pseudocapacitive materials has become the research hotspots currently [9], [10]. At the present time, graphene based binary electrode materials have been studied and fabricated widely [11], [12], [13], [14]. For example, our group has synthesized graphene/polyaniline hybrid electrode materials by in situ chemical polymerization and interface polymerization [15], [16]. The composites of graphene/MnO₂ with impressive electrochemical performance have been fabricated by Yu and his co-authors [17]. The improved electrochemical performance is attributed to the synergistic effect between graphene and conducting polymers or metal oxides.

Among the studied conducting polymers, PEDOT, as a member of polythiophene family, has been applied in the electrode materials because of its high conductivity, fast charge/discharge ability, wide potential window, and good environmental [18], [19], [20]. However, the drawbacks of poor cycling stability restrict its application in high energy and power devices. To improve the electrochemical performance of PEDOT, most studies based on carbon materials and PEDOT have been reported currently. For instance, Han et al. prepared graphite oxide/PEDOT composites as an electrode material for supercapacitor applications by in situ polymerization [21]. The higher capacitance retention of graphite oxide/PEDOT suggested higher cycle stability compared with PEDOT. Sun et al. [22] synthesized Graphene/PEDOT hybrids as electrode material of supercapacitor under microwave heating. The maximum capacitance can reach 270 F g⁻¹ at 1 A g⁻¹ using Graphene/PEDOT modified glass carbon electrode as the working electrode. PEDOT/GP/CC electrode material with a high specific capacitance value 126.23 F g⁻¹ was prepared using potentiostatic deposition by Chu et al. [23]. The SnO₂ is considered one of the most promising metal oxides due to its high capacitance, low cost and toxicity [24], [25], [26]. However, during the faradaic processes of pseudocapacitors, its poor electric conductivity and cycling performance caused by serious aggregation and considerable volume change upon cycling make SnO₂ undesirable for the industrial application in energy storage [27], [28]. The combination of SnO₂ with carbon materials used as electrode materials has been considered as an effective solution to improve the electrochemical performances due to the “cushion effect” of carbon component [29], [30], [31]. For example, Li et al. [32] fabricated graphene/SnO₂ nanocomposites by one-step method. The specific capacitance of the electrode materials was 34.6 F g⁻¹ at scan rate of 1 V s⁻¹. However, most of such composites are fabricated by solvothermal method or other complicated methods.

Since graphene, metal oxides and conducting polymers are the most important kinds of supercapacitor electrode materials, the reasonable and reliable combination of the three components would produce novel electrode materials with enhanced electrochemical performance. Nevertheless, to the best of our knowledge, there are few reports on graphene based ternary composites as supercapacitors electrode materials [33]. Recently, our group has reported several graphene based ternary composites for supercapacitors [34], [35], [36]. On the base of the previous work, herein, we introduced a simple one-pot approach for fabricating a novel GE/SnO₂/PEDOT ternary nanocomposite as an electrode material for supercapacitor. EDOT was dissolved in the acetonitrile which was miscible with water. And the aggregation of the graphene sheets was hold back by SnO₂ and PEDOT nanoparticles. The resulting ternary nanocomposite is demonstrated to be a promise electrode material with high energy and power, and good cyclability due to the synergetic effect among the three components.