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 hydro-chloride

The method of surface-enhanced Raman spectroscopy (SERS) was used to study the electrode processes at the interface between Al and ionic liquid. This method has great promise in the field of 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. Using the in situ SERS method, it was shown that with an increase in the cathodic polarization of the aluminum electrode, the intensity of the peaks associated with AlCl₄^– ion increases and the intensity of the peaks associated with Al₂Cl₇^– ion decreases. During anodic polarization of the electrode, the reverse process was observed: a decrease in the content of AlCl₄^– ions and an increase in the concentration of Al₂Cl₇^–. The concentrations of chloroaluminate anions in the near-electrode layer do 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 intensity of AlCl₄^– and Al₂Cl₇^– peaks on the electrode overpotential correlate with the stationary polarization curves. It has been experimentally proved that passivation of an aluminum electrode during anodic dissolution is caused by the formation of aluminum chloride on the electrode surface.

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