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  4. The role of phosphate additive in stabilization of sulphuric-acid-based vanadium(V) electrolyte for all-vanadium redox-flow batteries
 
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2017
Journal Article
Title

The role of phosphate additive in stabilization of sulphuric-acid-based vanadium(V) electrolyte for all-vanadium redox-flow batteries

Abstract
Catholyte in all-vanadium redox-flow battery (VRFB) which consists of vanadium salts dissolved in sulphuric acid is known to be stabilized by phosphoric acid to slow down the thermal aging at temperatures higher than 40 degrees C. To reveal the role of phosphoric acid, the thermally-induced aggregation is investigated using variable-temperature V-51, P-31, O-17, H-1 nuclear magnetic resonance (NMR) spectroscopy and dynamic light scattering (DLS). The results indicate that the thermal stabilization of vanadium(V) electrolyte is attained by the involvement of monomeric and dimeric vanadium(V) species in the reaction with phosphoric acid which is concurrent to the formation of neutral hydroxo-aqua vanadium(V) precipitation precursor. The dimers are stabilized by counter ions due to association reaction or if such stabilization is not possible, precipitation of vanadium pentoxide is favored. The evolution of particles size distributions at 50 degrees C in electrolyte samples containing 1.6 M vanadium and 4.0 M total sulphate and the pathways of precipitate formation are discussed. The optimal total phosphate concentration is found to be of 0.15 M. However, the induction time is assumed to be dependent not only on the total phosphate concentrations, but also on the ratio of total vanadium(V) to sulphate concentrations.
Author(s)
Roznyatovskaya, Nataliya  
Fraunhofer-Institut für Chemische Technologie ICT  
Roznyatovsky, Vitaly A.
Höhne, Carl-Christoph  orcid-logo
Fraunhofer-Institut für Chemische Technologie ICT  
Fühl, Matthias  
Fraunhofer-Institut für Chemische Technologie ICT  
Gerber, Tobias  
Fraunhofer-Institut für Chemische Technologie ICT  
Küttinger, Michael
Fraunhofer-Institut für Chemische Technologie ICT  
Noack, Jens  
Fraunhofer-Institut für Chemische Technologie ICT  
Fischer, Peter  
Fraunhofer-Institut für Chemische Technologie ICT  
Pinkwart, Karsten  
Tübke, Jens  
Journal
Journal of power sources  
Funder
Bundesministerium für Wirtschaft und Technolgie BMWi (Deutschland)  
DOI
10.1016/j.jpowsour.2017.07.100
Language
English
Fraunhofer-Institut für Chemische Technologie ICT  
Keyword(s)
  • vanadium redox-flow battery

  • electrolyte / sulfur ratio

  • thermally-induced ageing

  • phosphate additives

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