We employed voltammetry and scanning tunneling microscopy (STM) to study the coadsorption of mercaptoacetic acid (MAA) and cupric ions (Cu2+) on Au(111) electrode from 0.5 M sulfuric acid + 0.8 M CuSO4 + 0.03 mM MAA. Irreversibly adsorbed Cu2+ ions were reduced at 0.27 V first then at-0.2 V (vs. Ag/AgCl), ascribed to the underpotential and overpotential deposition processes, respectively. Counting the amount of charge involved in the stripping peak of the Cu deposit rendered quantification of Cu2+ ions codeposited with MAA on the Au(111) electrode, which yielded roughly 7.7 × 1014 Cu2+ ions/cm2. MAA alone and MAA + Cu2+ were adsorbed in Au(111)-(3 × √ 13) and (p × √ 3) structures, respectively. Cu2+ could be imaged by the STM, but their high mobility made it difficult to obtain high-quality STM results needed to quantify the amount of adsorbed Cu2+. Spatial structures of MAA molecules segregated onto the Cu deposit were found to vary with potential. They returned to the Au(111) electrode once the Cu deposit was oxidized at E > 0.4 V, yielding MAA + Cu2+ structures different from those seen at the pristine sample.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry