Probe the Dynamic Adsorption and Phase Transition of Underpotential Deposition Processes at Electrode-Electrolyte...

Area of Science:

• Electrochemistry
• Surface Science
• Materials Science

Background:

• Understanding electrode/electrolyte interfaces is critical for electrochemical applications.
• Copper underpotential deposition (UPD) on gold surfaces is a model system for studying interfacial phenomena.
• Phase transitions during UPD influence electrochemical reaction kinetics and surface properties.

Purpose of the Study:

• To reveal the static phase and phase transition of copper UPD on a gold electrode.
• To visualize the disintegration of the copper UPD adlayer and identify associated phase transitions.
• To elucidate the role of coadsorbed sulfate ions in the copper UPD process.

Main Methods:

• Electrochemical scanning tunneling microscopy (EC-STM) for direct visualization of adlayer structure.
• Electrochemical quartz crystal microbalance (E-QCM) for in situ mass and charge measurements.
• Density functional theory (DFT) calculations for atomic-level understanding of adsorption and bonding.

Main Results:

• EC-STM directly visualized the disintegration of the (√3 × √3)R30° copper UPD adlayer with coadsorbed sulfate.
• Phase transition between ordered (Phase II) and disordered (Phase III) copper UPD adlayers was observed.
• DFT calculations revealed sulfate binding via three oxygen atoms to copper bridge sites above vacancies.

Conclusions:

• Complementary in situ techniques (EC-STM, E-QCM) combined with DFT provide a comprehensive understanding of UPD dynamics.
• The study successfully characterized the dynamic interfacial adsorption and phase transitions during copper UPD on gold.
• This integrated approach offers a powerful strategy for investigating complex electrode surface processes.