Nuclear magnetic resonance studies on vanadium(IV) electrolyte solutions for vanadium redox flow battery

• Published in: Journal of power sources Vol. 195; no. 22; pp. 7709 - 7717
• Main Authors: Vijayakumar, M., Burton, Sarah D., Huang, Cheng, Li, Liyu, Yang, Zhenguo, Graff, Gordon L., Liu, Jun, Hu, Jianzhi, Skyllas-Kazacos, Maria
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.11.2010; Elsevier
• Subjects: 17O NMR; Anion exchanging; Applied sciences; Battery; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electrolytes; Environmental Molecular Sciences Laboratory; Exact sciences and technology; Molecular dynamics; NMR; Nuclear magnetic resonance; Solvents; Spectroscopy; Sulfates; Vanadium; Vanadium Redox Flow Battery; Vanadyl ion; Water exchange reaction; Molecular dynamics; 17O NMR; Water exchange reaction; Vanadium redox flow battery; Vanadyl ion; Electrolyte solution; Molecular dynamics method; Vanadium; Redox flow battery; O NMR; Exchange reaction; Nuclear magnetic resonance
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2010.05.008

The vanadium(IV) electrolyte solutions with various vanadium concentrations are studied by variable temperature 1H and 17O nuclear magnetic resonance (NMR) spectroscopy. The structure and kinetics of vanadium(IV) species in the electrolyte solutions are explored with respect to vanadium concentration and temperature. It was found that the vanadium(IV) species exist as hydrated vanadyl ion, i.e. [VO(H 2O) 5] 2+ forming an octahedral coordination with vanadyl oxygen in the axial position and the remaining positions occupied by water molecules. This hydrated vanadyl ion structure is stable in vanadium concentrations up to 3 M and in the temperature range of 240–340 K. The sulfate anions in the electrolyte solutions are found to be weekly bound to this hydrated vanadyl ion and occupies its second-coordination sphere. The possible effects of these sulfate anions in proton and water exchange between vanadyl ion and solvent molecules are discussed based on 1H and 17O NMR results.