Analysis of the effect of hydrogen-evolving side reaction in the aqueous aluminum-air battery

In this study, aqueous aluminum-air battery is revisited to analyze the effect of parasitic hydrogen generation which is one of challenging issues preventing it from full application even though it has outstanding benefits such as high theoretical energy density, low cost of system, environmental friendly and safe operation. The effect of hydrogen-evolution is studied systematically through component-level experiment to measure H2 evolution and ionic conductivity in the various electrolyte concentrations, and also through physics-based mathematical modeling to analyze the cell behavior coupled with electrochemical reaction and bubble dynamics. It is found that dominant loss in the aqueous aluminum-air battery is associated with kinetic loss affected by the parasitic hydrogen-evolving side reaction and the bubble shielding effect on the electrode, and the loss is found to be controlled by electrolyte velocity and concentration of OH−. The results of this study provide physical insight to understand the nature of generation, growth, and departure of gas bubbles from the electrode. Moreover, this research elucidates the effect of bubbles on the electrochemical reaction and factors to control their impact on the cell performance. Therefore, it is expected that the results of this study will act as key information to advance the understanding of characteristic electrochemical reactions in gas evolving electrodes.