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

Lu, Yi-Ting ORCID: 0000-0003-2128-1385, Neale, Alex R ORCID: 0000-0001-7675-5432, Hu, Chi-Chang and Hardwick, Laurence J ORCID: 0000-0001-8796-685X
(2021) Trapped interfacial redox introduces reversibility in the oxygen reduction reaction in a non-aqueous Ca2+ electrolyte. CHEMICAL SCIENCE, 12 (25). pp. 8909-8919.

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Electrochemical investigations of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been conducted in a Ca<sup>2+</sup>-containing dimethyl sulfoxide electrolyte. While the ORR appears irreversible, the introduction of a tetrabutylammonium perchlorate (TBAClO<sub>4</sub>) 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<sup>2+</sup> and TBA<sup>+</sup> cations to interact with generated superoxide (O<sub>2</sub> <sup>-</sup>). When TBA<sup>+</sup> is in larger concentrations, and large reductive overpotentials are applied, a quasi-reversible OER peak emerges with repeated cycling (characteristic of formulations without Ca<sup>2+</sup> cations). <i>In situ</i> 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 <i>trapped interfacial redox</i>. The first electrochemical step involves generation of O<sub>2</sub> <sup>-</sup>, followed primarily by partial passivation of the surface by Ca <sub><i>x</i></sub> O <sub><i>y</i></sub> product formation (the dominant initial reaction). Once this product matrix develops, the subsequent formation of TBA<sup>+</sup>--O<sub>2</sub> <sup>-</sup> is contained within the Ca <sub><i>x</i></sub> O <sub><i>y</i></sub> product interlayer at the electrode surface and, consequently, undergoes a facile oxidation reaction to regenerate O<sub>2</sub>.

Item Type: Article
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 28 May 2021 10:48
Last Modified: 26 Jan 2023 01:41
DOI: 10.1039/d0sc06991d
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