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Flow Battery Electroanalysis 2: Influence of Surface Pretreatment on Fe(III/II) Redox Chemistry at Carbon Electrodes

preprint
submitted on 24.09.2018 and posted on 25.09.2018 by Tejal Sawant, James McKone

Redox flow batteries are attractive for large-scale electrochemical energy storage, but sluggish electron transfer kinetics often limit their overall energy conversion efficiencies. In an effort to improve our understanding of these kinetic limitations in transition metal based flow batteries, we used rotating-disk electrode voltammetry to characterize the electron-transfer rates of the Fe3+/2+ redox couple at glassy carbon electrodes whose surfaces were modified using several pre-treatment protocols. We found that surface activation by electrochemical cycling in H2SO4(aq) electrolyte resulted in the fastest electron-transfer kinetics: j0 = 0:90 mA/cm2 in an electrolyte containing 10 mM total Fe. By contrast, electrodes that were chemically treated to either remove or promote surface oxidation yielded rates that were at least an order of magnitude slower: j0 = 0:07 and 0:08 mA/cm2, respectively. By correlating these findings with X-ray photoelectron spectroscopy data, we conclude that Fe3+/2+ redox chemistry is catalyzed by carbonyl groups whose surface concentrations are increased by electrochemical activation.

Funding

Swanson School of Engineering, University of Pittsburgh

History

Email Address of Submitting Author

tvs8@pitt.edu

Institution

University of Pittsburgh

Country

United States of America

ORCID For Submitting Author

0000-0003-4517-789X

Declaration of Conflict of Interest

Authors declare no conflicting interests

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