Observation of electrochemical reactions at Zn electrodes in Zn-air secondary batteries

The anode is the compartment for energy storage in Zn-air secondary batteries. In contrast, the cathode has no storage material but catalyzes the conversion of oxygen to hydroxide and vice versa. Because the composition of the anode varies with the state of charge, the potential of the battery reflects the composition of the materials in the anode. H-2 evolution, corrosion, and zincate/ZnO formation occur at the anode during battery operation and have a negative effect on battery performance. Consequently, reducing these adverse reactions by manipulating one of the reaction parameters, such as the concentration of OH-, can improve performance. In addition, the influence of KOH concentrations ranging from 2.0 to 8.0 M on these reactions is studied. We found that 4.0 M KOH is the optimum concentration for both redox reactions (Zn2+/Zn) and suppression of the anode corrosion rate. However, the higher conductivity obtained with 6.0 M KOH is appropriate when a faster reaction is needed, including suppression of negative effects. In particular, suppression of ZnO formation is advantageous, decreasing both resistance and H-2 evolution in the cell. (C) 2016 Published by Elsevier Ltd.