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Vanadium electrolyte for all-vanadium redox-flow batteries: The effect of the counter ion

 
: Roznyatovskaya, Nataliya; Noack, Jens; Mild, Heiko; Fühl, Matthias; Fischer, Peter; Pinkwart, Karsten; Tübke, Jens; Skyllas-Kazacos, Maria

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Volltext ()

Batteries 5 (2019), Nr.1, Art. 13, 16 S.
ISSN: 2313-0105
Englisch
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer ICT ()

Abstract
In this study, 1.6 M vanadium electrolytes in the oxidation forms V(III) and V(V) were prepared from V(IV) in sulfuric (4.7 M total sulphate), V(IV) in hydrochloric (6.1 M total chloride) acids, as well as from 1:1 mol mixture of V(III) and V(IV) (denoted as V3.5+) in hydrochloric (7.6 M total chloride) acid. These electrolyte solutions were investigated in terms of performance in vanadium redox flow battery (VRFB). The half-wave potentials of the V(III)/V(II) and V(V)/V(IV) couples, determined by cyclic voltammetry, and the electronic spectra of V(III) and V(IV) electrolyte samples, are discussed to reveal the effect of electrolyte matrix on charge-discharge behavior of a 40 cm2 cell operated with 1.6 M V3.5+ electrolytes in sulfuric and hydrochloric acids. Provided that the total vanadium concentration and the conductivity of electrolytes are comparable for both acids, respective energy efficiencies of 77% and 72–75% were attained at a current density of 50 mA∙cm−2. All electrolytes in the oxidation state V(V) were examined for chemical stability at room temperature and +45 °C by titrimetric determination of the molar ratio V(V):V(IV) and total vanadium concentration.

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