Recent progress in the synthesis of graphene/CNT composites and the energy-related applications

doi:10.1016/j.jmst.2019.05.063

Abstract

Abstract:

Graphene and carbon nanotube (CNT) are representative carbon nanomaterials which have aroused numerous research interest due to their extraordinary material properties and promising application potentials, especially in the energy storage and conversion areas. However, the agglomeration happening in these materials has largely blocked their applications. Hybridization of CNT with graphene can, on one hand, prevent the agglomeration behavior, on the other hand, generate a synergistic effect between them with enhanced physical and chemical properties. There have been many studies conducted to find out the suitable approaches to synthesize graphene/CNT composites, and realize the application potentials of these structures. Based on the recent advances, this paper reviews the current research progress that has been achieved in synthesizing graphene/CNT composites, and the energy-related applications. Through this review, we aim at stimulating more significant research on this subject.

Key words: Graphene, Carbon nanotube, Composites, Synthesis methods, Energy-related applications

Xin Wu, Fengwen Mu, Haiyan Zhao. Recent progress in the synthesis of graphene/CNT composites and the energy-related applications[J]. J. Mater. Sci. Technol., 2020, 55: 16-34.

Figures/Tables 14

Fig. 1. Three types of graphene/CNTs composites.

Fig. 2. Synthesis of graphene/CNTs composites through the CVD method. (a-b) Multi-layered graphene/aligned multi-walled CNTs structure, and (c) the corresponding formation mechanism [45]. (d-e) 3D graphene/CNT sandwich structure and (f) the illustration of formation process [46].

Fig. 3. Growth of CNTs on top and bottom sides of graphene. (a) The synthesis mechanism. (b-c) The characterization of the as-synthesized T-CNT/graphene/B-CNT structure, in which the dashed line marks the top/bottom interface where the graphene layer resides. Part of the graphene component is marked by a dashed rectangle in (c) [63].

Fig. 4. LBL assembly of the graphene/CNT composite films through (a-c) electrostatic interactions[83] and (d-f) van der Waals interactions [91]. (a) and (d) are the mechanisms of the electrostatic assembly and van der Waals assembly, (b-c) and (e-f) are the corresponding microstructure images.

Fig. 5. (a) Illustration of the process to make a FLG/MWCNT composite paper. Scanning electron microscope (SEM) images of FLG/MWCNT hybrid papers with (b) FLG/MWCNT = 5/1 and (c) FLG/MWCNT = 1/3[102].

Fig. 6. Graphene/CNTs composite films by EPD. (a) Schematic representation of the EPD process. Images of the samples (b) dispersed in solution and (c) after EPD. (d-e) Typical FESEM images of the composite films with various graphene/CNT weight ratios. (f) Typical HRTEM image of the composite film [121].

Fig. 7. Synthesis of rGO/CNT/NF hybrids by combined EPD and CVD methods. (a) Illustration of the synthesis process, (b) TEM image of the 3D rGO/CNTs composite [129].

Fig. 8. Synthesis of rGO/MWCNTs composites by in situ chemical reduction. (a) The preparation processes. (b) Electron mediating properties of rGO-MWCNTs/glassy carbon electrode. (c) SEM image of the rGO/MWCNTs. (d) 2D atomic force microscope (AFM) image and (e) 3D AFM image of rGO/MWCNTs films [133].

Table 1 Comparison of different methods for the preparation of graphene/CNT composites.

Methods	Description	Advantages	Disadvantages
CVD	Catalytic conversion of carbon gaseous precursor into solid carbon materials by using catalyst	High efficiency, directness, high yield, good repeatability, good controllability	Long processing time, and high working temperature. PECVD has high requirements for the carbon source and can release toxic gas.
LBL	Composite films are formed by depositing alternating layers which are interacted through molecular interactions or electrostatic interactions	Simple, robust, low cast. The multifunctional properties of the composites can be easily and accurately controlled by adjusting the solution environment.	It's hard to achieve 3D hybrid nano-architectures. And the residual charged functional groups would response to the applied electrical field, which influences the device properties.
VF	Vacuum filtering the carbon suspension onto a filtration membrane, followed by membrane dissolution and substrate transfer	Simple and fast. The as synthesized membrane is uniform. The thickness of the membrane could be accurately controlled	The filtering speed will be largely reduced with the increase of layer number, which limits the application in membrane with large thickness.
EPD	The suspended graphene/CNT particles are impelled from the suspension medium to the substrate by an electric field	Versatile, low cost, high deposition rate. The prepared films are uniform with large scale and controlled thickness	The properties depend on the quality of the graphene/CNT suspension and the surface clearness of the substrate
ISR	Reducing the combined GO/CNT solution to obtain the rGO/CNT composites	Facile, inexpensive, with mass production capability	It’s a challenge to achieve the GO/CNTs solution with well- defined compositions. The residual functional groups would degrade the properties

Table 1 Comparison of different methods for the preparation of graphene/CNT composites.

Methods	Description	Advantages	Disadvantages
CVD	Catalytic conversion of carbon gaseous precursor into solid carbon materials by using catalyst	High efficiency, directness, high yield, good repeatability, good controllability	Long processing time, and high working temperature. PECVD has high requirements for the carbon source and can release toxic gas.
LBL	Composite films are formed by depositing alternating layers which are interacted through molecular interactions or electrostatic interactions	Simple, robust, low cast. The multifunctional properties of the composites can be easily and accurately controlled by adjusting the solution environment.	It's hard to achieve 3D hybrid nano-architectures. And the residual charged functional groups would response to the applied electrical field, which influences the device properties.
VF	Vacuum filtering the carbon suspension onto a filtration membrane, followed by membrane dissolution and substrate transfer	Simple and fast. The as synthesized membrane is uniform. The thickness of the membrane could be accurately controlled	The filtering speed will be largely reduced with the increase of layer number, which limits the application in membrane with large thickness.
EPD	The suspended graphene/CNT particles are impelled from the suspension medium to the substrate by an electric field	Versatile, low cost, high deposition rate. The prepared films are uniform with large scale and controlled thickness	The properties depend on the quality of the graphene/CNT suspension and the surface clearness of the substrate
ISR	Reducing the combined GO/CNT solution to obtain the rGO/CNT composites	Facile, inexpensive, with mass production capability	It’s a challenge to achieve the GO/CNTs solution with well- defined compositions. The residual functional groups would degrade the properties

Fig. 9. (a) Illustration of the EDLC based on crumpled graphene ball/ porous CNT composites [58]. (b) Illustration of the ion diffusion behavior for the graphene nanomesh/CNT composites and (c) the capacitance properties of the electrode based on graphene nanomesh/CNT composites [109].

Fig. 10. (a) Fabrication of graphene/CNT composite counter electrode and (b-c) the performance of the cells based on CNT, graphene/CNT, graphene, Pt counter electrodes. GC37 refers to 30 wt% graphene and 70 wt% MWCNTs, and GC73 refers to 70 wt% graphene and 30 wt% MWCNTs [184].

Fig. 11. (a) Transparent conductive electrode based on PEDOT:PSS/G:SWCNT and (b) the corresponding conductivity and (c) transmittance of the composite electrode[200].

Fig. 12. (a) CVD preparation process of graphene/CNTs composites and (b) the micro-image of the composites, (c) the LIBs performance based on composite anode[216].

Fig. 13. (a) Pt/rGO-CNTs composites and (b-c) the corresponding cell performance for PEMFCs[251].

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