Fabrication of Three-Dimensional Cu/CNT Composite Film By Electrodeposition

Abstract

Introduction Three-dimensional metallic materials have large surface area and high electrical conductivity, and have thus attracted attention as electrode materials for applications such as lithium-ion batteries, electric double-layer capacitors and electrochemical sensors. Methods such as de-alloying1) and electrodeposition with a template2,3) are generally used in the fabrication of three-dimensional metallic materials. These methods, however, take great deal of times and costs. Our laboratory has reported that a three-dimensional copper structure can be simply fabricated by electrodeposition from a copper sulfate plating bath containing polyacrylic acid.4) The fabrication of thicker three-dimensional structures is desirable in order to obtain larger surface areas, though the thickness of the three-dimensional structure was only approximately several micrometers.In addition, the three-dimensional structure has low strength because it is composed of a thin copper sheet. Therefore, the three-dimensional structure could be deformed in the case of thickening the structural layer. Carbon nanotubes (CNTs) are expected to be applied in a wide range of fields. We consider that the embedding of CNTs into the copper sheets in the three-dimensional structure by means of electroplating can reinforce the structural integrity even when thickened. Therefore, in this study, the fabrication of a three-dimensional Cu/CNT composite film by electrodeposition was attempted to realize reinforcement of the three-dimensional structure and an increased surface area. Experimental A copper plating bath for three-dimensional copper film was prepared by the addition of polyacrylic acid (M.W. 5000) to a copper sulfate bath (0.85 M CuSO4·5H2O + 0.55 M H2SO4). The plating bath for the three-dimensional Cu/CNT composite film was prepared by the addition of CNTs (VGCF, Showa Denko) to the previous copper plating bath. The plating bath was treated with an ultrasonic homogenizer to disperse the CNTs. The dispersibility of the CNTs was examined by a laser diffraction particle size analyzer. Electrodeposition was performed under galvanostatic conditions at 25 °C. Pure copper plate was used as the cathode and a phosphorus-containing copper plate was used as the anode. Phase analysis of the deposits was performed using X-ray diffraction (XRD). The surface and cross-sectional morphology were observed using field–emission scanning electron microscopy (FE-SEM). Results and Discussion The measured particle size distribution suggests that the CNTs are dispersed as primary particles in the plating bath. Therefore, the dispersibility of the CNTs in the plating bath is considered to be very good. Fig. 1(a) shows cross-sectional SEM images of plated films fabricated from the plating baths containing 0 g/L CNTs. The structure is deformed, and it has lost the space between the copper sheets that constitute the three-dimensional structure. Fig. 1(b) shows the plated film fabricated from the plating bath containing 10 g/L CNTs. The spaces between the copper sheets are maintained. For this reason, the addition of CNTs to the three-dimensional copper structure is considered to be effective for reinforcement of the structure. References 1) T. Song, M. Yan, Z. Shi, A. Atrens, and M. Qian, Electrochim. Acta, 164, 288–296 (2015). 2) B. Qi, H. Yang, K. Zhao, M. M. Bah, X. Bo, and L. Guo, J. Electroanal. Chem., 700, 24–29 (2013). 3) H. Zhang, Q. Pan, and H. Zhang, Mater. Lett., 106, 360–362 (2013). 4) S. Arai and T. Kitamura, ECS Electrochem. Lett., 3 (5), D7-D9 (2014). Figure 1