Adsorption of 4,4′-bipyridine on the Cd(0001) single crystal electrode surface

In situ scanning tunneling microscopy (STM), electrochemical impedance spectroscopy have been applied to study the adsorption of 4,4′-bipyridine (4,4′-BP) on the Cd(0001) single crystal electrode from 0.1 M Na₂SO₄ + 1.0×10^-5 M H₂SO₄ + x M 4,4′-BP aqueous solutions (x from 0.0 to 3.0×10^-3). Influence of the electrode potential (E) on the adsorption characteristics of 4,4′-BP on Cd(0001) has been demonstrated. Two regions with low capacitance values have been observed in the series capacitance vs. E curve. The in situ STM data revealed that 4,4′-BP forms a stripe pattern on the Cd(0001) single crystal electrode surface. The results of density functional theory (DFT) calculations and surface enhanced infrared adsorption spectroscopy data have been applied in order to establish the adsorption layer structure and possible orientation of the 4,4′-BP molecules on the Cd(0001) surface. DFT calculations, used to compliment the experimental data, demonstrate the importance of the van der Waals interactions for the formation of the stripe pattern.