Sulfate-Source-Dependent Anodic Discharge and Apparent Corrosion Response of Al Alloy Electrodes in Alkaline Electrolytes.

Anodic corrosion of Al alloy electrodes limits their use as anodes in alkaline aluminum-air batteries. Na2SO4- and Al2(SO4)3-containing formulations were compared at matched nominal sulfate-group inputs but different formulation-derived Na and Al inputs. Aqueous 2 M NaOH was mixed with 0.3 M Na2SO4 or 0.1 M Al2(SO4)3 solution at NaOH:additive-solution volume ratios of 7:3, 5:5, and 3:7, and Al-Mg-Sn-Gd-P alloy electrodes were evaluated in a three-electrode configuration. All galvanostatic tests passed the same external charge of 160 mAh. Mass-loss-normalized anodic charge (QΔm) is reported as an operational metric normalized by the net post-discharge electrode mass decrease, not as conventional battery capacity or efficiency. The Al2(SO4)3-containing formulations showed higher QΔm values; at the 3:7 ratio, QΔm increased from 917 to 1894 mAh g-1. Potentiodynamic polarization yielded lower polarization-derived apparent corrosion current densities and higher polarization resistances, while potentiostatic electrochemical impedance spectroscopy showed larger interfacial impedance responses in the Al2(SO4)3-containing series. Scanning electron microscopy showed electrolyte-dependent post-discharge morphologies. These results establish sulfate-source-dependent differences in anodic, polarization, impedance, and morphological responses under matched nominal sulfate-group input without isolating the effect of a single Na- or Al-containing species, establishing the presence or chemical identity of a distinct interfacial film, or demonstrating improved full-cell performance.