Electro-Formation of Cu-Graphene Composites and Its Property Evaluation

Abstract

In the current study, few-layer graphene particles (FLGPs) have been synthesized by electrochemical exfoliation method. Two different electrolytes of 1M H2SO4 and HNO3 were used. The electrolyte produces anions of 2 4 SO and 3 NOwhich interact with pyrolytic graphite sheets to intercalate and produce FLGPs. Further, the prepared FLGPs are reduced by ascorbic acid and hydrazine hydrate and are leveled as RFLGPs(Vc) and RFLGPs(Hy) respectively. The prepared graphene particles were then analyzed by various scientific analyses such as TGA, XRD, FTIR, XPS, UV and Raman spectroscopy.
Thermal stability and yield of graphene particles are done by TGA analysis. XRD and Raman spectroscopy were used for structural properties, lattice spacing and crystal structure of graphene particles. The (001) and (002) lattice plane of graphene oxide and graphene has been observed at 13º and 26.2º from XRD analysis. The as-synthesized graphene were expected to be functionalized which was confirmed by FTIR analysis and the functional groups are hydroxy, carboxy, epoxides and alcohol. The prepared FLGPs were then analyzed by XPS to quantify carbon oxygen ratio. The electronic transitions of π-π* and n-π* have been analyzed by UV-visible spectra. The topographical and morphological analysis of graphene has been carried out by FESEM and TEM analysis.
The FESEM microscopy shows the agglomeration and layer structure. The TEM analysis gives the number of layers of graphene particles. The in-house synthesized graphene was found to consist of few layers and was partially functionalized too. The prepared FLGPs and RFLGPs have been used as reinforcement with the copper matrix to synthesize Cu- FLGPs nanocomposite.
Copper-graphene nano-composites were synthesized by the electrodeposition method.
FLGPs and RFLGPs of different concentrations (0.1, 0.3 and 0.5 g/L) were added into the copper matrix. The Cu films are plated first onto the steel substrate at different temperatures (25, 20 and 15 °C) to decide the deposition temperature (based upon the film characteristics obtained). Synthesis of the composite films were then carried out and compared in both silent and ultrasonic stirring conditions in the aqueous electrolyte. Cu deposited at 15 °C was best and was chosen to carry out the composite film deposition.
The synthesized specimens (Cu and composite films) were characterized by surface Profilometry, XRD, SEM, EDS and AFM analyses. Furthermore, the distribution of
Xi graphene was found to be better in the presence of ultrasound as witnessed from the structural and micro-graphical analysis. Then after the micro and nano-mechanical as well as electrical resistivity properties of the composites were measured to evaluate the performance of the films. The composite films have 31% improved hardness as compared to the pure copper films. The electrical resistivity has been increased from 1.6×10-6 -cm to 3.6×10-6 -cm. The electrodeposited Cu-FLGPs composite shows improved mechanical and comparable electrical properties as well as compared to the pure copper thin film. The Cu-RFLGPs composite shows 38% higher hardness as compared to pure copper thin film. The Cu-RFLGPs composites did show an adhesive type of wear leading to delamination of Cu layers. Apart from mechanical properties, the electrical resistivity of the sono-electroplated films was found to be improved as well. The corrosion behaviors of Cu-FLGPs as well as Cu-RFLGPs composite films have been analyzed by threeelectrode cell setup. Tests were carried out in two solutions i.e. standard borate buffer and 3.5% NaCl to simulate the general and pitting corrosion behavior respectively. All the composite films show well developed passivation regions in borate buffer and the pitting was also evident from the potentio-dynamic polarization plots. The general corrosion tendency and rate was found to be less in composite films. Further pitting was also less in composite films. The mechanism of such observation was proposed by EIS study. Out of the two types, Cu-RFLGPs composites have superior mechanical, electrical and anticorrosive properties.