Cu/graphene composite coatings electrodeposited in a directly dispersed graphene solution after electrochemical exfoliation with enhanced oxidation resistance

https://doi.org/10.1016/j.jallcom.2021.160706Get rights and content

Highlights

  • Graphene is electrochemically exfoliated and directly dispersed in a CuSO4/DMF/H2O solution without adding a surfactant.

  • Cu/graphene composite coatings are plated in the graphene dispersions without collection and addition of graphene.

  • The co-deposited graphene has an effect on reducing oxidation degree of the Cu/graphene composite coatings.

Abstract

Directly dispersing graphene in aqueous solutions, without chemical treatment or adding surfactants, remains an obstacle for plating metal-graphene composite coatings. In this study, graphene was prepared by electrochemical exfoliation of a graphite anode and directly dispersed in N, N-dimethylformamide (DMF)/H2O solutions containing CuSO4 (40, 80, and 120 g/L) without adding a surfactant. Cu/graphene composite coatings were electrodeposited in graphene dispersions. The Cu/graphene composite coating with the highest graphene content was obtained in a solution with 80 g/L CuSO4. The co-deposited graphene affected the preferred orientation and led to a different oxidation reaction rate between the Cu/graphene composite coatings. After thermal treatment, the Cu/graphene composite coating plated in the solution with 80 g/L CuSO4 exhibited the lowest oxidation degree. This indicates that co-deposited graphene reduces the oxidation degree of Cu/graphene composite coatings.

Introduction

Cu-based materials have extensive electronic applications owing to their superior electrical conductivity, thermal conductivity, and ductility. In addition, their alloys have been widely used in machine manufacturing [1]. Cu-matrix composites have become increasingly popular in the past decade, owing to their enhanced mechanical, electrical, and thermal properties, allowing for varied applications. In recent years, numerous Cu-matrix composites have been synthesized with different reinforcements such as Al2O3 [2], SiO2 [3], TiO2 [4], carbon nanotubes [5], and graphene [6]. Among these, graphene has attracted significant attention.

Graphene, a single layer of sp2-bonded carbon atoms bonded in a hexagonal lattice, has stimulated a vast amount of research [7]. The remarkable properties of graphene, include a high Young’s modulus, fracture strength, thermal conductivity, mobility of charge carriers, and specific surface area [8], [9], [10], [11], [12]. It also exhibits interesting transport phenomena, such as the quantum Hall effect [13]. Due to its excellent properties, graphene has been utilized in many areas, such as the photoelectric field. Graphene related composites, including the X-ray photon response, tunable photoluminescence, and light-controlled conductive switching have been investigated in some notable works [14], [15], [16]. As an ideal reinforcement, graphene can improve the hardness, tensile strength, ductility, corrosion resistance, and wear resistance of the metal-based composites [17], [18]. Graphene or graphene oxide can be prepared in various ways, such as mechanical [19], [20], chemical [21], or electrochemical [22] exfoliation. There are several limitations associated with chemical and mechanical routes for producing graphene, including time-consuming laborious procedures, high operating temperatures, and aggressive reagents. All these flaws contribute to relatively high costs related to the industrial production. Electrochemical approaches exhibit considerable advantages over non-electrochemical methods. They are typically conducted via a single step, facile to operate, and can be conducted under ambient conditions. Furthermore, electrochemical approaches can be performed on the order of minutes to hours, in contrast to mechanical and chemical routes which are usually cost for days [23]. Among these, electrochemical exfoliation is one of the most promising methods for large-scale production of graphene.

In recent years, the growth of Cu/graphene composite coatings by electrodeposition has attracted significant interest. Jagannadham showed an improvement in the thermal [24] and electrical [25] conductivities of electrodeposited Cu/graphene composite coatings. Xie et al. [26] synthesized reduced graphene oxide (rGO)/Cu composite films as potential electrical contact materials using an electrochemical deposition method. Nevertheless, previous investigations on the properties of Cu/graphene composite coatings have mainly focused on the electrical conductivity or mechanical strength, and the oxidation of electrodeposited Cu/graphene composite coatings has rarely been reported. The introduction of graphene can change the microstructure and orientation of the metal grains in the composite coating. Therefore, it is reasonable to predict that co-deposited graphene in a Cu/graphene composite coating can reduce the oxidation degree of the coating.

Despite extensive studies on the preparation of Cu/graphene composite coatings, some notable problems remain unsolved. There are two main issues in the electrodeposition of Cu/graphene composite coatings. First, it is difficult to directly achieve a homogeneous dispersion of graphene in an aqueous plating solution and a metal matrix. Graphene flakes with a 2D nature, large surface area, and high surface energy are very prone to irreversible aggregation or re-stacking. Thus, their homogeneous dispersion is extremely difficult to achieve using traditional mixing methods. In addition, graphene materials are usually derived from rGO, which has severe structural defects introduced during the exfoliation and reduction process, leading to poor structural stability [27]. The one-step method of preparing and dispersing graphene in a plating solution for co-deposition with metal ions is a promising and facile technique for the electrodeposition of graphene-reinforced metal-matrix coatings. Additionally, it allows graphene to be directly dispersed without using surfactants. Its simplicity makes it suitable for large-scale production without requiring volatile solvents or reducing agents [28].

In this study, graphene was synthesized by electrochemical exfoliation in CuSO4/N, N-dimethylformamide (DMF)/H2O solutions with different CuSO4 contents and directly dispersed for subsequent electrodeposition. Cu/graphene composite coatings were then plated on Cu foil in graphene dispersions. The co-deposition of graphene leads to a change in the micromorphology and preferred orientation of the composite coatings by affecting the nucleation of Cu during electrodeposition. The Cu coatings and Cu/graphene composite coatings were thermally treated in an air atmosphere to investigate the effect of graphene on the oxidation of the coatings. The Cu/graphene composite coating plated in the solution with 80 g/L of initial CuSO4 content possessed the largest amount of co-deposited graphene and lowest atomic percentage of CuO. Therefore, co-deposited graphene decreases the oxidation degree of Cu/graphene composite coatings.

Section snippets

Electrochemical exfoliation and electrodeposition

Electrochemical exfoliation was performed using a two-electrode system. A graphite plate was used as the anode and carbon source, whereas Cu foil was used as the cathode. DMF and deionized water were mixed in a volume ratio of 1:1. CuSO4 was then dissolved in the DMF/H2O solutions to form electrolyte concentrations of 40, 80, and 120 g/L. The electrochemical exfoliations were conducted under a DC voltage of 10 V for different durations (90, 180, and 270 min). After sonication for 30 min,

Characterization of graphene anodic exfoliation and cathodic polarization

The products electrochemically exfoliated from the graphite anode and collected from the suspensions were characterized to ascertain the feasibility of directly obtaining graphene dispersions for plating Cu/graphene composite coatings in one solution. The electrochemically exfoliated graphene was directly dispersed into the DMF/H2O solutions because of the low surface energy of DMF. Meanwhile, the H2O in the solutions ensured the transportation of the ions, and electrochemical exfoliation of

Conclusions

Electrochemically exfoliated graphene was directly dispersed in CuSO4/DMF/H2O solutions without chemical treatment or adding a surfactant. The electrodeposition was subsequently conducted in graphene dispersions, and Cu/graphene composite coatings were successfully obtained. The co-deposited graphene led to a variation in the crystal surface orientation before changing the rate of oxidation of the Cu/graphene composite coatings. After thermal treatment, the Cu/graphene composite coatings

CRediT authorship contribution statement

Xinyu Mao: Investigation, Methodology, Writing - original draft. Liqun Zhu: Conceptualization. Huicong Liu: Methodology. Haining Chen: Writing - review & editing. Wen Li: Writing - review & editing. Rui Cao: Writing - review & editing. Weping Li: Funding acquisition.

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

This work was supported by National Key Research and Development Program of China (2018YFB2002000) and National Natural Science Foundation of China (51971012).

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