Rotating ring-disk electrode studies of copper electrodeposition and electrodissolution in acid copper sulfate

A rotating ring-disk electrode was used to investigate the effects of Cl{dollar}sp-,{dollar} organic additives (thiourea, benzotriazole and a proprietary brightener), and mass transfer on Cu electrodeposition and electrodissolution in acid CuSO{dollar}sb4{dollar} solutions. The dependence of deposit appearance on deposition potentials, organic additives, Cl{dollar}sp-{dollar} and hydrodynamic conditions has also been investigated.; Four distinct regions--the Tafel, transition, limiting current and post limiting current regions--were observed during cathodic polarization of Cu between the open circuit potential and {dollar}-{dollar}1.2 V (vs. SCE). On the other hand, three distinct regions--the Tafel, transition and current plateau regions--were observed during anodic polarization of Cu between the open circuit potential and {dollar}+{dollar}1.3 V (vs. SCE). Characteristic ring current behavior observed during cathodic and anodic polarizations of Cu supported the two-step mechanism for Cu electrodeposition and electrodissolution in acid CuSO{dollar}sb4{dollar} with Cu{dollar}sp+{dollar} as an intermediate. The "critical" Cl{dollar}sp-{dollar} concentration to begin formation of CuCl is estimated to be between 30 and 40 mg/L.; Bright Cu deposits were not obtained with thiourea (TU) or the proprietary brightener (PB) alone, but in conjunction with Cl{dollar}sp-{dollar} and agitation. Benzotriazole(BTA)-containing acid CuSO{dollar}sb4{dollar} also required agitation, but the presence of Cl{dollar}sp-{dollar} was detrimental to the deposition of bright Cu deposits. The conditions for bright Cu deposits were Reynolds number (Re) {dollar}ge{dollar} 140, 0.29 {dollar}le{dollar} i/i{dollar}rmsb{lcub}L{rcub}{dollar} {dollar}le{dollar} 0.45 and 50 mg/L (1.4mM) Cl{dollar}sp-{dollar} in TU-containing acid CuSO{dollar}sb4;{dollar} Re {dollar}ge{dollar} 140, 0.22 {dollar}le{dollar} i/i{dollar}rmsb{lcub}L{rcub}{dollar} {dollar}le{dollar} 0.49 in Cl{dollar}sp-{dollar}-free BTA-containing acid CuSO{dollar}sb4;{dollar} and Re {dollar}ge{dollar} 140, 0.14 {dollar}le{dollar} i/i{dollar}rmsb{lcub}L{rcub}{dollar} 0.67 and 10-50 mg/L Cl{dollar}sp-{dollar} in PB-containing acid CuSO{dollar}sb4.{dollar}; The brown film formed on Cu in the anodic transition region by the disproportionation reaction, 2Cu{dollar}sp+{dollar} = Cu {dollar}+{dollar} Cu{dollar}sp{lcub}2+{rcub},{dollar} limited increases in ring currents with increase in potential but did not affect the disk current. The fluctuations in ring current in the transition region are attributed to the instability of the loosely adherent brown film. The minimum in disk current at the end of the transition region is attributed to precipitation of a CuSO{dollar}sb4{dollar} salt film. In the current plateau region, Cu electrodissolution was controlled by mass transfer of Cu{dollar}sp{lcub}2+{rcub}{dollar} from the disk. The presence of 100-5000 mg/L Cl{dollar}sp-{dollar} in acid CuSO{dollar}sb4{dollar} significantly decreased disk currents due to precipitation of a CuCl film. The presence of BTA decreased disk and ring currents in the Tafel and "lower" transition regions, but no substantial change was observed by addition of either TU or PB. The addition of 10-50 mg/L Cl{dollar}sp-{dollar} to BTA-containing acid CuSO{dollar}sb4{dollar} further decreased disk and ring currents in the transition and current plateau regions, unlike the effect of Cl{dollar}sp-{dollar} at these low concentrations on Cu electrodissolution in either TU- or PB-containing solutions.