EVALUATION OF ALLOY ANODES FOR ALUMINUM-AIR BATTERIES .4. ELECTROCHEMICAL IMPEDANCE ANALYSIS OF PURE ALUMINUM IN 4M-KOH AT 25-DEGREES-C

An electrochemical impedance analysis of pure aluminum in 4M KOH at 25°C is reported. Impedance spectra have been obtained at 30-80 mV intervals extending from the hydrogen evolution region at -1.96V(vs. Hg/HgO, 4M KOH) to the transpassive dissolution region at -1.35V. The impedance spectra are found to consist of two intersecting capacitive semicircles with a loop at intermediate frequencies. The impedance spectra and the steady-state current/voltage characteristics (including the partial anodic and cathodic curves) are accounted for by a model involving the stepwise addition of hydroxyl groups to surface aluminum atoms, culminating in the chemical dissolution of Al(OH)3 to form Al(OH)4-.