Highly reversible oxygen to superoxide redox reaction in a sodium-containing ionic liquid

Comprehensive studies regarding the impact of the electrolyte composition on the oxygen reduction mechanism are important to deliver highly efficient rechargeable sodium–air batteries. Thus, we report, for the first time, the oxygen reduction mechanisms and discharge products in a pyrrolidinium-based ionic liquid in the presence of different Na⁺ ion concentrations. Upon increasing the Na⁺ salt concentration, oxygen reduction becomes more efficient (e.g. 74%) and the onset potential of the reduction process shifts to a more positive value due to superior solvation of the superoxide anion by Na⁺. These observations should provide a platform of potential electrolytes for Na–air batteries.