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Trapped interfacial redox introduces reversibility in the oxygen reduction reaction in a non-aqueous Ca2+ electrolyte

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Abstract

Electrochemical investigations of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been conducted in a Ca2+-containing dimethyl sulfoxide electrolyte. While the ORR appears irreversible, the introduction of a tetrabutylammonium perchlorate (TBAClO4) 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 Ca2+ and TBA+ cations to interact with generated superoxide (O2). 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 Ca2+ cations). In situ 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 trapped interfacial redox. The first electrochemical step involves generation of O2, followed primarily by partial passivation of the surface by CaxOy product formation (the dominant initial reaction). Once this product matrix develops, the subsequent formation of TBA+--O2 is contained within the CaxOy product interlayer at the electrode surface and, consequently, undergoes a facile oxidation reaction to regenerate O2.

Graphical abstract: Trapped interfacial redox introduces reversibility in the oxygen reduction reaction in a non-aqueous Ca2+ electrolyte

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Article information


Submitted
23 Dec 2020
Accepted
28 May 2021
First published
28 May 2021

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2021, Advance Article
Article type
Edge Article

Trapped interfacial redox introduces reversibility in the oxygen reduction reaction in a non-aqueous Ca2+ electrolyte

Y. Lu, A. R. Neale, C. Hu and L. J. Hardwick, Chem. Sci., 2021, Advance Article , DOI: 10.1039/D0SC06991D

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