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Lookup NU author(s): Dr Jochen Friedl,
Professor Ulrich Stimming
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND).
The VO2+/VO2+ redox reaction takes place in the catholyte solution of the all-vanadium redoxflow battery (VRFB), one of the few options to electrochemically store energy fromintermittent renewable sources on a large scale. However, the sluggish redox kinetics of theVO2+/VO2+ couple limit the power density of the VRFB, which increases the footprint of thepower converters and increases capital costs. Therefore, catalysis of the redox reaction anda deeper understanding of its intricate reaction pathways is desirable.The kinetics of the VO2+/VO2+ redox reaction have been investigated in 1M sulfuric and 1 Mphosphoric acid by cyclic voltammetry, chronoamperometry, electrochemical impedancespectroscopy and flow battery tests. It was found that in 1 M phosphoric acid the electrontransfer constant k0 is up to 67 times higher than in 1 M sulfuric acid. At higher overpotentialsthe determined currents match for the two electrolytes. This over-potentialdependent difference in electron transfer constant is explained by variable contributionsfrom three reaction mechanisms for the oxidation of VO2+ to VO2+, and by the presence ofadsorbed intermediates for the reduction of VO2+. This study shows that the redox kineticsof the VO2+/VO2+ can be considerably accelerated by altering the chemical environment ofthe vanadium ions, and that this effect can also be transferred into a flow battery.
Author(s): Holland-Cunz M, Friedl J, Stimming U
Publication type: Article
Publication status: Published
Journal: Journal of Electroanalytical Chemistry
Print publication date: 15/06/2018
Online publication date: 28/10/2017
Acceptance date: 26/10/2017
Date deposited: 30/10/2017
ISSN (print): 1572-6657
ISSN (electronic): 1873-2569
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