Abstract
Earlier research has shown that supersaturated vanadium sulfate electrolytes can remain stable for an extended time ranging from hours to days making them suitable for electrochemical energy storage applications. This study investigates the electrochemical characteristics of supersaturated vanadium IV and V sulfate solutions and the solvation structures of molecules in these solutions. The electrochemical characterizations, e.g., OCV, constant current/voltage/overpotential oxidation, and reduction, reveal that supersaturated V(IV) and V(V) solutions contain electrochemically active ions, inactive-but-convertible molecules, and inactive-and-unconvertible molecules. The chemical conversion rate from inactive-but-convertible molecules to active ions is high enough to maintain a constant active ions concentration during the electrochemical reactions. Possible structures and the relationship of these structures to their electrochemical activity at supersaturated levels were discussed. The inactive-but-convertible molecules are suggested to be the agglomerates of the individual dissociated vanadium ion pairs, while the inactive-and-unconvertible molecules consist of undissociated vanadium salt molecules with the sulfate anions bonded directly to the vanadium cations. This work also found that preparation methods (with or without preheating the electrolyte during synthesis) and the oversaturation level can affect the composition of the molecules in the electrolyte.
Publisher
The Electrochemical Society
Subject
Materials Chemistry,Electrochemistry,Surfaces, Coatings and Films,Condensed Matter Physics,Renewable Energy, Sustainability and the Environment,Electronic, Optical and Magnetic Materials