Aluminum Activation in Ionic Liquids

Aluminum (Al) is the third most abundant element (after oxygen and silicon) and the most abundant metal in Earth's crust. Al is quite remarkable as it holds a low density and it has the ability to resist corrosion due to surface passivation. This passivation layer protects Al from corrosion in a relatively wide range of pH and potentials. Nevertheless, in aqueous media, the layer is vulnerable in both highly acidic and basic environments, leading to rapid corrosion reactions. As an anodic material, Al has a theoretical gravimetric capacity of 2.98 Ah/gr and its volumetric capacity is as high as 8.1 Ah/cm³. For the sake of comparison, Li metal holds capacities of 3.86 Ah/g and 2.06 Ah/cm³, respectively. 

In non-aqueous media electrochemical dissolution of Al is partly hampered due to inefficient and thus insufficient passivation layer removal prior to any current application. Similar issues pertain when the non- aqueous solutions employed are Room Temperature Ionic Liquids (RTIL).  In the present work an activation of Al was studied in EMIm(HF)_2.3F RTIL. For this specific electrolyte it was already established that electrochemical dissolution of Al occurs, in considerable rates, sufficient for application in Al-Air batteries ^[1]. The alteration of the surface, as detected by FTIR, XPS and STEM, suggests on the formation of passivating Al-O-F compounds on the surface, instead of native oxide passivation. The source of this specific activation is established in this work, and the surface of Al prior to and following activation was identified. The applied methodology was also used for identification and study of Al activation in other family of RTILs. The preliminary results of this specific electrochemical system will be also presented.

^[1] D. Gelman, B. Shvartsev, Y. Ein-Eli, J. Mater. Chem. A. 2.47 (2014) 20237-20242.