Abstract

The behavior of molecules at the electrochemical interface was probed using infrared visible sum frequency generation spectroscopy (SFG).

The corrosion inhibitor benzotriazole (BTAH) adsorbed on Cu(100) and Cu(111) in acidic solution demonstrates potential dependent behavior that is correlated with order in the adsorbed layer of benzotrialzole anion (BTA ^-). The ordered adlayer consists of the BTA^- in two configurations: one coordinated to both the surface and Cu+ ions and the second coordinated only to the surface. The BTA- coordinated to Cu+ is shown to be more stable to Cl^- addition than BTA^- coordinated to only the surface.

In situ Surface Enhance Raman Scattering, SFG, Electrospray Ionization Mass Spectrometry, and detailed calculations are used to examine the interaction of bis-(3-sulfopropyl)-disulfide (SPS) and mercaptopropylsulfonic acid (MPS) with Cu surfaces both in the absence and presence of Cl-. In the presence of Cl^-, no evidence for an adsorbed Cu-thiolate complex is observed; however, the data supports the formation of a sulfonate-CuCl complex. Our results suggest the additive's thiolate moiety is unnecessary for the acceleration behavior observed.

At the Ag-water interface in NaF and KF electrolyte solutions, water is observed in environments associated with both the electrode surface and the diffuse double layer. Peaks are observed that are correlated with low-order water, water interacting with electrolyte ions, specifically adsorbed water to the electrode surface, and hydronium. Spectra obtained from a thiol-modified Ag surface enable discrimination between surface-bound water and that in the double layer. Potential dependent spectra show the intensities of specifically adsorbed and ion solvating water diminish near the pzc.

SFG in tandem with electrochemical capacitance and CV measurements are used to study the effects of applied potential on the adsorption and orientation of PABA at a Ag(111) surface. The data indicates that PABA changes orientation in response to the charge on the electrode surface, orienting one way positive of the potential of zero charge (pzc) and oppositely negative of the pzc. At positive potentials a phase change is observed associated with the formation of a condensed layer. These results show that the orientation of small molecule zwitterions can be controlled by applied potential.