Analytical determination of water effects on the anodic dissolution of aluminum in nonaqueous electrolytes

Abstract

Several analytical techniques are used to probe the influence of water concentration on the electrochemical behavior of aluminum anodes in Al/ active-non-aqueous electrolytes. Normally passive, Al exhibits facile electrochemical oxidation in both AlCl3/γ-butyrolactone (AlCl3/BLA) and in (C2H5)4NCl acetonitrile (TEAC/ACN) electrolytes. However, in these two electrolytes, the influence of water on Al oxidation is opposite. FTIR spectra, parasitic water reduction reactions, surface microscopy and electrolytic conductivity were conducted to probe competing water activation or water passivation effects on organic phase Al electrochemistry. Incremental increase from 0 to 1.5 M H2O (0 to 3% water by volume) hinders Al oxidation in 1 M AlCl3/BLA, increasing polarization from 100 mV to 400 mV cm2 mA-1. Yet in 0.3 M TEAC/ACN, Al is passive in the absence of water, exhibiting currents only in the μA cm-2 domain, equivalent to oxidative polarization losses of over 1000 mV cm2 mA-1. This polarization is alleviated with water addition, and decreases from 20 mV to 7 mV cm2 mA-1, as water is increased from 0.3 to 1.5 M.