Application of in situ Surface-Enhanced Raman Spectroscopy for Investigation of Electrode Processes at the Interface of an Aluminum Electrode with a Chloroaluminate Ionic Liquid Based on Triethylamine Hydrochloride

Surface-enhanced Raman spectroscopy (SERS) was used to study electrode processes at the interface between Al and an ionic liquid. This method has great promise for studying electrochemical processes, since it allows one to determine the composition of the electrolyte in a thin near-electrode layer during electrode polarization. It was demonstrated that aluminum has SERS-activity in a chloroaluminate ionic liquid based on Et₃NHCl. It was shown using in situ SERS that the intensity of peaks associated with the \({\text{AlCl}}_{4}^{-}\) ion increased and the intensity of peaks associated with Al₂\({\text{Cl}}_{7}^{-}\) ion decreased upon increasing the cathodic polarization. The reverse process was observed during anodic polarization of the electrode, i.e., the content of \({\text{AlCl}}_{4}^{-}\) ions decreased and the concentration of Al₂\({\text{Cl}}_{7}^{-}\) increased. The concentrations of chloroaluminate anions in the near-electrode layer did not change at cathodic overpotentials above the overpotential of reaching the limiting current and at anodic overpotentials above the passivation overpotential. The obtained dependences of the relative intensities of \({\text{AlCl}}_{4}^{-}\) and Al₂\({\text{Cl}}_{7}^{-}\) peaks on the electrode overpotential correlated with the stationary polarization curves. It was experimentally proved that passivation of an aluminum electrode during anodic dissolution was caused by the formation of aluminum chloride on the electrode surface.