Exploring the Relationship of Structure and Electrochemical Activity of V（Ⅲ） Ion in Vanadium Electrolyte

All-vanadium redox flow battery（VRFB） is one of the most promising large-scale energy storage technologies,owing to its inherent safety and long service life.During the charging-discharging process,the redox reaction of V（Ⅲ）↔V（Ⅱ） with standard electrode potential of-0.25 V（vs.NHE） is the main electrochemical reaction in negative electrolyte.The side reaction of hydrogen evolution would take place with low electrochemical activity of V（Ⅲ） ion,which will degrade VRFB performance.In present work,to explore the relationship of structure and electrochemical activity of V（Ⅲ） ion,the quantum chemistry calculation and activity analysis of V（Ⅲ） ions with various structures were conducted with the MP2 theoretical method and LANL2 DZ basis using the Gaussian software.Combining to the experimental results of electrochemical activity,the low electrochemical activity of V（Ⅲ） ion in fresh prepared electrolyte was found due to their hydrolytic polymerization.,The polymerization can be reduced by 5 cycles of charge and discharge,which leads to a high electrochemical activity of V（Ⅲ） ion and inhibition of hydrogen evolution.But the electrochemical activity of activated electrolyte will obviously reduce after 40 days’ standing at room temperature,indicating that the hydrolytic polymerization of V（Ⅲ） ions in negative electrolyte may be spontaneous.