Combined Effect of Dissolved Oxygen and pH in Aqueous Electrolytes on Zn-Anode Corrosion Behavior in Aqueous Zn-Ion Batteries

Aqueous Zn-ion batteries (AZIBs) have recently emerged as an appealing option for grid scale energy storage due to their distinct advantages in safety, cost, and materials sustainability. However, cycle instability caused by the interactions between Zn-anode and electrolyte solutions (aka Zn corrosion) has been a critical issue hindering the commercial development of AZIBs. To bridge this technical gap, we herein present a fundamental study to delineate the important role that the much-neglected dissolved oxygen played in Zn anode corrosion reaction along with pH. Oxygen reduction reaction (ORR) is proposed as a parallel pathway to the commonly perceived hydrogen evolution reaction (HER) in the Zn-anode corrosion mechanism. To prove this new ORR mechanism, we systematically dissolved oxygen and pH in the model ZnSO4 electrolyte along with current density/polarity and examine the resultant surface morphologies, compositions, gas evolution, electrode overpotential, and cycle stability of Zn-anode. We conclude that the dissolved oxygen-dependent ORR pathway can compete with the pH-dependent HER pathway in the formation of the surface passive layer, making a marked impact on the overpotential and stability of the Zn-anode. The lowest overpotential and longest cycle stability are observed in a ZnSO4 electrolyte with the lowest dissolved oxygen.