UC Irvine

Electrification, especially in transportation, is key to objectives mitigating climate change effects. Metal-air batteries, including aluminum-air batteries (AAB), may offer performance and safety improvements over lithium-air batteries by using widely available, inexpensive materials.AAB cell advantages in weight, cost, and safety are countered by high polarization from a persistent oxide film, and by high corrosion rates, most notably in alkaline electrolytes. Much research on these topics has employed pure aluminum or specially prepared alloys to minimize corrosion during experimental evaluation. A key question - could commercial aluminum alloys be used in AAB cells in the immediate future? Thus, twin purposes of this study were to assess the state of current technologies of aluminum-air batteries, and to characterize several commercial aluminum alloys to gauge their suitability for use with common aqueous electrolytes in AAB cells. A comprehensive review of prior AAB works was conducted, including assessments of several other metal-air technologies where common elements, such as catalysts for the oxygen reduction reaction (ORR), are relevant. Effects of anode material composition, and of electrolyte additions as corrosion inhibitors, were considered. Characterization of Al alloy 6061 in alkaline electrolyte was done by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy. The cathodic effect of second-phase intermetallic particles in Al 6061 to spur galvanic corrosion nearly negated inhibitor benefit in 4M sodium hydroxide electrolyte. Detailed experimental studies were conducted in neutral and acidic aqueous electrolytes. Aluminum alloys 4047 (silicon), 6061 (magnesium/silicon), and 7075 (zinc/copper) were evaluated by half-cell electrochemical techniques, and by use in a flow battery cell coupled to platinum-cobalt or iron-nitrogen-carbon catalysts in air-breathing or oxygen-breathing gas diffusion electrodes (GDE). Post-discharge characterization of anode surfaces was done using scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction. Each alloy manifested different performance, but the strongest influence on cell performance came from ORR kinetics in the GDE. Cell outputs and aluminum utilizations for all materials were similar, regardless of composition. Given the state of the art in ORR catalysts, this work indicates that there appears to be no impediment to using commercial alloys as anode materials in AAB systems at this time.