Stability of aluminium in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and ethylene glycol mixtures

The stability of electrochemically passivity aluminium has been investigated in mixtures of ethylene glycol, 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid, Na2B4O7.10H2O and NaH2PO4. The effects of (i) borax and sodium dihydrogen phosphate salts presence, (ii) water absorption and (iii) ethylene glycol content are studied by electrochemical impedance spectroscopy (EIS). The results show a decrease in the polarization resistance and an increase in the capacitance associated with the passive oxide dielectric properties with an increase in the water and/or ethylene glycol content in the mixtures. The presence of Na2B4O7.10H2O and NaH2PO4 salts stabilize the oxide layer.

Research highlights
► The Al anodic film is stable in BMI.BF4 ionic liquid.
► The solution resistance diminishes when ethylene glycol (EG) is added on BMI.BF4.
► The capacitance of Al anodic film increases in wet BMI.BF4 and EG mixtures.
► The Al anodic film resistance diminishes in wet BMI.BF4 and EG mixtures.
► Borate and phosphate stabilize the Al anodic film in wet electrolyte environment.