An investigation of the adsorption of pyrazine and pyridine on nickel electrodes by in situ surface-enhanced Raman spectroscopy

This paper describes a surface-enhanced Raman spectroscopic study on nickel electrodes. The enhancement factor of the roughened Ni substrate was found to be from two to three orders, depending on the surface pre-treatment. High-quality SERS spectra of pyrazine and pyridine were obtained at different potentials. The bands assigned to Ni–Npyrazine and Ni–Npyridine were observed around 260 cm−1 in the low-frequency region of two sets of SERS spectra, respectively. The adsorption behaviour of pyrazine and pyridine on Ni electrode was studied and compared based on the surface selection rule. The result suggests that both pyrazine and pyridine were strongly adsorbed onto the substrates. It also implies that pyridine was adsorbed perpendicularly onto the substrate, while pyrazine adsorbed onto the substrate in a slightly tilted vertical configuration. The observation of forbidden bands of the pyrazine molecule is due to the lowering of the symmetry from D2h to C2V when adsorption onto the surface takes place. The electrochemical reduction of pyrazine on the Ni electrode was observed at extremely negative potentials in the presence of Cl−.