The oxygen paradox in alkaline zinc-air batteries creates radical-induced anodic corrosion

<h2>Summary</h2> Can the fuel in use adversely affect the performance of an energy storage system? Here, oxygen (O₂) in zinc-air (O₂) batteries (ZABs) is shown to adversely impact the anodic process, leading to early cell failure, though its amount limiting can affect the cathodic reaction kinetics. A chemical reduction of dissolved O₂ on metallic Zn in alkaline medium produces superoxide radicals (O₂^·¯), revealed by electron paramagnetic resonance (EPR) and hydrodynamic voltammetry. This triggers ZnO passivation on Zn in O₂, causing cell death. Despite a similar discharge time, ZnO passivation occurred faster in an O₂-rich than in an O₂-free environment. Cell design modification limiting O₂ availability at the anode extended cyclability by 5 times at high current density, enhancing specific capacity. This study reveals a new parasitic O₂ reduction process on Zn, causing surface modification and passivation, posing a greater issue than the hydrogen evolution reaction (HER). It underscores the need to inhibit cathodic O₂ crossover in ZABs.