Electrochemical behavior of aluminum in triethylamine hydrochloride–aluminum chloride ionic liquid

Abstract

This paper studies the electrochemical behavior of aluminum in AlCl₃–Et₃NHCl with a molar ratio of AlCl₃ to Et₃NHCl (N) from 1.3 to 1.95 by stationary electrolysis and electrochemical impedance spectroscopy. Cathodic and anodic stationary polarization curves are obtained. The cathodic polarization curves are S-shaped and contain limiting current plateau sections. Salt passivation is observed at anodic overpotentials. Apparent exchange current densities were measured for the first time and were found to increase from 1.02 to 2.50 mA cm⁻² with an increase in Al₂Cl₇⁻ concentration. The apparent electrochemical rate constant and transfer coefficient at T = 303 K were calculated (1.14 × 10⁻⁶ cm s⁻¹ and 0.14, respectively). Apparent exchange current densities at the Al|AlCl₃–Et₃NHCl interface are determined at temperatures between 303 and 373 K (N = 1.5), and the data are used to calculate the apparent electrochemical rate constant (2.6 × 10⁻⁶ to 10⁻⁶ cm s⁻¹); the activation energy for the charge transfer process was also determined (31.4 kJ mol⁻¹). The results obtained in this paper may be used to optimize the composition of electrolytes in aluminum-ion batteries and also to further investigate the processes taking place in chloroaluminate ILs.