Study of Electrochemical Mechanisms and Interactions of Bis(3-sulfopropyl)-disulfide on the Cu-Electrodeposited Polythiophene Interface

Direct electroplating has become a key method for polymer metallization due to simplicity and efficiency, but achieving uniform metal deposition on conductive polymers remains challenging. This study investigates the mechanism of copper (Cu) electrodeposition on the surface of conductive polythiophene (PTh), with a particular focus on the role of the additive bis(3-sulfopropyl)-disulfide (SPS) in the process of pulse electroplating. Wide-frequency attenuated total reflection surface-enhanced infrared absorption spectroscopy (wf-ATR-SEIRAS) was performed to explore the interaction between SPS and PTh. Further analysis combined with density functional theory (DFT) calculations indicated that the SO3– groups in the SPS molecule tend to adsorb onto the S atoms of the PTh chain through electrostatic interactions and dipole–dipole interactions, facilitated by the alignment of the −SO3– group with the electron-rich sulfur atoms on the PTh surface. In addition, the additive SPS significantly accelerates the Cu deposition rate on the PTh surface without chloride ions (Cl–), thus circumventing the need for the synergistic effect of chloride during conventional copper electroplating. Specifically, when SPS was introduced into the Cu electroplating process on PTh interfaces, the absolute current increased from 1.8 to 3.3 mA, representing over 80% increase in the current. At the same time, the addition of SPS reduced the PTh interface impedance and enhanced charge transfer, which are directly correlated with the increased Cu deposition rate. This further demonstrates that SPS promotes the reduction of Cu2+ by enhancing the electron charge transfer between PTh and Cu2+. This study provides a molecular-level understanding of the interaction between SPS and PTh and offers insights into the reaction mechanism of SPS on Cu electrodeposition on PTh.