The effect of hydrogen co-deposition on the morphology of copper electrodeposits. II. Correlation between the properties of electrolytic solutions and the quantity of evolved hydrogen N.D. Nikolic ´ a, * , G. Brankovic ´ b , M.G. Pavlovic ´ a , K.I. Popov a,c a ICTM-Institute of Electrochemistry, University of Belgrade, Njegoševa 12, P.O.B. 473, 11001 Belgrade, Serbia b Institute for Multidisciplinary Research, Kneza Viseslava 1a, 11030 Belgrade, Serbia c Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, P.O.B. 3503, 11001 Belgrade, Serbia article info Article history: Received 1 February 2008 Received in revised form 20 March 2008 Accepted 9 April 2008 Available online 18 April 2008 Keywords: Electrodeposition Scanning electron microscope (SEM) Copper Sulfuric acid Hydrogen evolution abstract Formation of irregular deposits by electrodeposition from acid sulfate solutions of various H 2 SO 4 concen- trations was examined by the determination of the average current efficiency of hydrogen evolution and by the scanning electron microscopic (SEM) analysis of the copper deposits morphology. Copper den- drites were the dominant morphological form obtained at overpotentials corresponding to the plateaus of the limiting diffusion current density. The number of the formed dendrites was increasing with the decreasing H 2 SO 4 concentration. Holes formed due to the attached hydrogen bubbles were the basic mor- phological form of electrodeposited copper from all analyzed copper sulfate solutions at overpotentials outside the plateau of the limiting diffusion current density. The honeycomb-like structures (holes of the detached hydrogen bubbles with cauliflower-like agglomerates of copper grains between them) were formed if electrodepositions were performed from 0.15 M CuSO 4 in both 0.250 M and 1.0 M H 2 SO 4 . On the other hand, aside from the holes and cauliflower-like forms, electrodeposition from 0.15 M CuSO 4 in 0.125 M H 2 SO 4 led to the formation of degenerated dendrites and dendritic particles inside channels formed of evolved hydrogen. Holes with shoulders of degenerated dendrites were also formed. The for- mation of different morphological forms under hydrogen co-deposition was discussed in the terms of hydrodynamic conditions in the near-electrode layer using the values for the break-off diameter of hydrogen bubbles. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Various irregular morphological forms of metal deposits, such as dendrite, needle, spongy, fibrous, honeycomb-like structure, etc., can be formed by electrodeposition processes [1–7]. These forms may be either useful (the production of powders [8,9], the creation of open and porous structures suitable for electrodes in electrochemical devices [5–7,10]) or undesirable (in electrowining and electrorefining processes, in batteries [3]). In case of copper, irregular or disperse deposits are formed at current densities and overpotentials which belong to the plateau of the limiting diffusion current density and at higher ones, where parallel to copper elec- trodeposition hydrogen evolution reaction occurs. The examination of the effect of hydrogen co-deposition on a morphology of electrodeposited copper has been initiated recently [5–7,9,11–13]. The special attention has been paid to the formation of both electrodes for electrochemical devices (denoted as honey- comb-like structures) [5–7,11–13] and powder particles in a potentiostatic regime of electrolysis [9]. According to these results, the shape of obtained morphological forms strongly depends on the quantity of evolved hydrogen. For example, the honeycomb- like structure was obtained only under a quantity of evolved hydrogen which was enough high to change hydrodynamic condi- tions in the near-electrode layer. The concept of ‘‘effective overpo- tential‘‘ was proposed to explain the formation of this structure [5]. On the other hand, powder particles can be either dendritic (if par- ticles are formed with a quantity of evolved hydrogen below the critical value for the change of hydrodynamic conditions) or cauli- flower-like ones (if they were formed with a quantity of evolved hydrogen above this value) [9]. The most often used electrolytes for electrodeposition of copper are those based on aqueous solutions of sulfuric acid (H 2 SO 4 ) and cupric sulfate (CuSO 4 ) [14]. The main species present in a sulfuric acid aqueous solutions containing Cu 2+ ions are: bisulfate ion (HSO  4 ), cupric ion (Cu 2+ ), aqueous cupric sulfate (CuSO 4(aq) ), hydrogen ion (H + ), and sulfate ion (SO 2 4 ) [15–17]. Pitzer‘s model [18] was used to calculate the equilibrium of the CuSO 4 –H 2 SO 4 – H 2 O system in a wide range of concentrations and temperatures [17]. This was done in order to estimate conditions occurring in 0022-0728/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2008.04.006 * Corresponding author. Tel./fax: +381 11 337 03 89. E-mail address: nnikolic@tmf.bg.ac.yu (N.D. Nikolic ´). Journal of Electroanalytical Chemistry 621 (2008) 13–21 Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem