Effect of Hydrogen Evolution on Current Distribution during Electrodeposition at Vertical Electrodes

Experiments were carried out at vertical sectioned electrodes on which copper was deposited in the presence of simultaneous hydrogen evolution. By measurement of copper deposited on each electrode section, it was possible to ascertain the local rate of each electrode reaction. The influence of hydrogen evolution on the rate of copper deposition supported the interpretation that two kinds of mass transfer effects occur simultaneously. In one, bubbles produced locally cause stirring on detachment while, in the other, bubbles produced below the point of interest rise upward and thereby cause stirring. A mathematical model was developed to predict the current distribution in cells having nonuniform potential fields. The model included ohmic resistance of electrolyte, Tafel kinetics for hydrogen evolution, mass transfer for copper deposition, and the particular cell geometry under study. Calculations agreed to within 20% of experimental data.