Trapped interfacial redox introduces reversibility in the oxygen reduction reaction in a non-aqueous Ca electrolyte.

Electrochemical investigations of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been conducted in a Ca-containing dimethyl sulfoxide electrolyte. While the ORR appears irreversible, the introduction of a tetrabutylammonium perchlorate (TBAClO) co-salt in excess concentrations results in the gradual appearance of a quasi-reversible OER process. Combining the results of systematic cyclic voltammetry investigations, the degree of reversibility depends on the ion pair competition between Ca and TBA cations to interact with generated superoxide (O ). When TBA is in larger concentrations, and large reductive overpotentials are applied, a quasi-reversible OER peak emerges with repeated cycling (characteristic of formulations without Ca cations). Raman microscopy and rotating ring-disc electrode (RRDE) experiments revealed more about the nature of species formed at the electrode surface and indicated the progressive evolution of a charge storage mechanism based upon . The first electrochemical step involves generation of O , followed primarily by partial passivation of the surface by Ca O product formation (the dominant initial reaction). Once this product matrix develops, the subsequent formation of TBA--O is contained within the Ca O product interlayer at the electrode surface and, consequently, undergoes a facile oxidation reaction to regenerate O.