Electrochimica Acta 56 (2011) 9397–9405 Contents lists available at ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Effects of (NH 4 ) 2 SO 4 and BTA on the nanostructure of copper foam prepared by electrodeposition DoHwan Nam, RyoungHee Kim, DongWook Han, JeongHan Kim, HyukSang Kwon ∗ Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 335 Gwahangno, Yuseong-gu, Daejeon, Republic of Korea a r t i c l e i n f o Article history: Received 24 May 2011 Received in revised form 13 July 2011 Accepted 6 August 2011 Available online 16 August 2011 Keywords: Copper foam Electrodeposition Porous structure Hydrogen evolution Chemical additive Mechanical property a b s t r a c t Copper foam with dendritic copper nanostructure was synthesized by an electrodeposition process using hydrogen bubbles as dynamic templates. To modify the morphology of the copper nanostructure in the foam walls, (NH 4 ) 2 SO 4 and BTA (benzotriazole) were introduced into the electrolytic bath as chemical additives, and their influences on the morphologies and the structural characteristics of copper deposits were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanical strength and stiffness of the copper foam were evaluated by the compression test. The corncob-like deposits of the copper foam were changed to needle-like nanodendrites by the addition of (NH 4 ) 2 SO 4 , which significantly improved the mechanical strength and stiffness due to the self-supporting effects of the tightly interlocked needle-like nanodendrites. In contrast, the copper foam prepared from the solution with (NH 4 ) 2 SO 4 and BTA shows high ductility but low mechanical strength due to the for- mation to grape-like copper deposits. Both the copper foams exhibited higher mechanical properties than the one with corncob-like deposits formed in the additive-free solution. The reaction mechanism of (NH 4 ) 2 SO 4 and BTA on the nanostructure of the copper foam at high cathodic current density was clarified by analyzing the effects of the additives on the copper deposition reaction and hydrogen gas evolution reaction, respectively. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Metallic foams have been investigated based on their specific structure, which exhibits extremely large surface area, low den- sity and high strength and stiffness. Recently, an interest in thin metallic foams has increased as the application of metallic forms has expanded to electrochemical devices such as energy absorbers, catalyst carriers, and electrodes for batteries. However, the con- ventional manufacturing processes for metallic foams, e.g., foaming with blowing agents and vapor deposition, are not appropriate for thickness and porosity control of the foams. Shin et al. [1–3] succeeded in fabricating thin copper foams by electrodeposition using hydrogen bubbles as a dynamic template with no polymer framework. This process has several advantages compared with conventional processes: low cost, simple bath preparation, easy thickness control, and no additional process to remove the polymer template. Since the copper foams are formed rapidly by extremely high cathodic potential, they have two inher- ent problems to be solved for wide applications: the first one is weak bonds between the foam structure and substrate, caus- ing the detachment of copper deposits from the substrate, and ∗ Corresponding author. Tel.: +82 423503326; fax: +82 423503310. E-mail address: hskwon@kaist.ac.kr (H. Kwon). the other is the weak mechanical strength or the brittleness of copper foam due to fragile copper deposits in the foam walls [4]. The mechanical strength of the copper foam prepared by the electrodeposition is greatly influenced by the structural morphol- ogy and density of the copper deposit. The major parameters affecting the morphology of the copper deposit are the cathodic overpotential [5], the composition of the electrolytic bath [6,7], and the solution temperature [8]. However, the morphology of copper deposits controlled by these parameters is not sufficient for the formation of the copper foam with high mechanical strength. Several research groups reported that using chemical additives is an effective way for controlling the size, shape, and density of copper deposits. When chlorine ions are added into an electrolytic bath, the size of copper deposits was reduced and the density of the copper deposits was increased as a result of accelerated deposition reactions [3]. Likewise, the addition of CTAB (cetri- monium bromide) as surfactant causes a size reduction and an increase in the density of copper deposits in the foam walls [7]. Kim et al. also demonstrated that PEG (polyethylene glycol) and MPSA (3-mercapto-1-propane sulfonic acid sodium salt), which are com- monly used as additives for copper electroplating, played a crucial role in forming 3D interconnected copper foams by changing the size, shape, and density of copper deposits [9]. Thus, it is antici- pated that mechanical properties of copper foam can be improved 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.08.025