Vanadium Electrolyte for All-Vanadium Redox-Flow Batteries: The Effect of the Counter Ion

• Published in: Batteries (Basel) Vol. 5; no. 1; p. 13
• Main Authors: Roznyatovskaya, Nataliya, Noack, Jens, Mild, Heiko, Fühl, Matthias, Fischer, Peter, Pinkwart, Karsten, Tübke, Jens, Skyllas-Kazacos, Maria
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 18-01-2019
• Subjects: Chloride; Chlorides; Conductivity; electrolyte; electrolyte stability; Electrolytes; Electronic spectra; Hydrochloric acid; Oxidation; Rechargeable batteries; Room temperature; Valence; Vanadium; vanadium redox reactions; vanadium redox-flow battery
• ISSN: 2313-0105; 2313-0105
• DOI: 10.3390/batteries5010013

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.