Depolarization of Cu Electrodeposition in the Presence of Ag: A Cyclic-Voltammetry Study

Abstract

During our investigation of Cu-Ag alloy electrodeposition from acidic sulfate bath, peculiar behavior of Cu reduction was found in the CV profiles when the Cu deposition overpotential is very small. An early Cu(II) reduction peak, which is revealed to be a full reduction of Cu(II) to Cu(0) based on the EQCM-CV measurement, was observed in addition to the main Cu(II)/Cu(0) deposition peak. To our surprise, this early Cu deposition peak occurs when the deposition bath contains Ag(I) cations, or the substrate contains Ag metals.EQCM-CV profile shows that the early Cu deposition peak is associated with a 65% deposition efficiency, slightly smaller than that of the main Cu(II)/Cu(0) reduction peak (~78%). The amount of Cu deposited associated with the early Cu reduction peak is estimated based on the total charge associated with this peak. The early Cu reduction peak is associated with Cu deposit thicker than 3 nm, with the thickness increases with decreasing scan rate or increasing Ag(I) concentration in the electrolyte. Meanwhile, from the CV profiles, the early Cu reduction peak is associated with a Tafel slope ~30mV/dec. We hypothesize that by the catalytic effect of Ag, either in the substrate or in the initial deposit, on the intermediate reduction step of Cu(II)/Cu(I) causes the early Cu reduction peak by shifting rate determining step of Cu(II)/Cu(0) deposition from Cu(II)/Cu(I) to Cu(I)/Cu(0). Disclaimer: This work has been submitted at Electrochimica Acta (manuscript id: EA21-4167RR1), with title "Depolarization of Cu electrodeposition in the presence of Ag: a cyclic-voltammetry study". Figure attached is chosen from this manuscript. Figure. Cyclic voltammograms at electropolished Cu substrate from 0.3 M CuSO4 + 0.5 M H2SO4 (a) with or without 0.5 mM NaNO3, and (b) with 0-0.5 mM AgNO3. Figure 1