Isomer-dependent adsorption of cyanopyridines on platinum probed by surface-enhanced Raman spectroscopy

The adsorption of three cyanopyridine isomers on Pt electrodes was investigated using electrochemical surface-enhanced Raman spectroscopy (SERS) within a wide potential region. It was revealed that the adsorption configurations depend on the applied potential and on the positions of CN group. The 4-cyanopyridine (4-CP) and 3-cyanopyridine (3-CP) molecules adsorb on Pt surfaces via the N atoms of the pyridine ring, while the 2-cyanopyridine (2-CP) molecules attach to the surface with the N atoms of both the pyridine ring and the CN group. In the case of 4-CP, the tilted adsorption mode is dominant under the potential of −0.8–0 V. It is converted to the vertical mode when the potential is moved to 0–0.8 V. For 3-CP, the vertical adsorption mode is found to be preferential in the full potential window. The CN stretching vibrational band of 2-CP is absent in the observed SER spectra. This is mainly caused by the characteristic π-electron delocalization as both N atoms are anchored to the Pt surface to form a heterogeneous ring. The hydrogen atoms are co-adsorbed with the cyanopyridine isomers on the Pt surface in extremely negative potential region.