Oxygen redox processes in PEGDME-based electrolytes for the Na-air battery

Abstract

We present the characterization by the rotating-disc-electrode (RDE) and cyclic-voltammetry (CV) methods of oxygen-reduction/oxygen-evolution (ORR/OER) processes in the Na-air battery containing fresh and aged polyethylene glycol dimethyl ether 500 (PEGDME500)-based electrolyte. It was found that the time of storage of this solvent affects the oxidation overpotentials of the reduction products. It is suggested that the reason for the PEGDME500 change originates from the synthesis process, in which the sodium alcoholate molecule can remain in the solvent. Insertion of metallic sodium prevents aging of PEGDME500. The results are compared with a tetraethylene glycol dimethyl ether (TEGDME)-based electrolyte. It was shown that the voltammogram of the TEGDME-based electrolyte is similar to that of the fresh PEGDME500, but with the opposite ratio of NaO2-to-Na2O2 oxidation currents. This indicates that Na2O2 is the main reduction product in TEGDME, and we suggest that in fresh PEGDME500, Na2O2 is formed by the chemical disproportionation of the dissolved NaO2 in the solution.