Growth of electrolytic copper dendrites. II: Oxalic acid medium

The growth of electrolytic copper dendrites between two coplanar copper discs, 250 μm in diameter, was investigated in oxalic acid medium by a technique based on the coupling of electrochemical measurements and microvideo optical in situ observations. The influence of the oxalic acid concentration, the potential difference applied between the two microelectrodes, and a laminar flow perpendicular or parallel to the electric field was investigated on the growth rate of the dendrites and on the short circuit time. It was shown that during the incubation time, the copper ions dissolved from the anode are transported to the cathode mainly by migration. The growth rate of the filamentary dendrites increases with the oxalic acid concentration, activation current, and potential. Then, various techniques able to eliminate, or at least to slow, the dendrite development were studied. The addition of a supporting electrolyte, buffered solutions, or inhibitors slows or eliminates the deposit growth. At the end, the influence of the size of the anion and of the presence of dissolved oxygen in the solution was examined. In particular, the absence of oxygen in the solution prevents the deposit growth at the time scale of the experiment as there is practically no cathodic reaction available during the incubation time to compensate the anodic dissolution current.