We
investigate the mechanism of 3-mercapto-1-propanesulfonate (MPS)
acceleration of Cu electrodeposition in the presence of Cl– through comparison with the inactive but related model compounds
1-butanesulfonate and 1-butanethiol (BuSH). In situ shell-isolated
nanoparticle-enhanced Raman spectroscopy was used to evaluate these
additives as a function of potential. MPS adsorbs to the Cu electrode
in the presence of Cl– through the thiol functional
group. Density functional theory calculations reveal that the adsorption
of thiol has a depolarizing effect on the strength of the interaction
between adsorbed Cl– and the electrode surface,
the consequences of which are observed spectroscopically. The sulfonate
moiety does not interact directly with the electrode. However, cyclic
voltammetry used to assess the permeability of adsorbed MPS and BuSH
adlayers indicates that the sulfonate group has a more direct role
in Cu deposition beyond simple disruption of the surface layer.
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