An image analysis-based method to determine the vanadium electrolyte contents during the capacity recovery process with a facile chemical oxidation strategy

Repairing and regenerating the unbalanced electrolytes is critical for the long-term operation of vanadium redox flow batteries (VRFBs). In this work, we propose a simple strategy to repair the unbalanced electrolytes for capacity recovery through chemical oxidation with the V(V) electrolyte and develop a method based on image analysis to obtain the electrolytes’ V(IV) ion contents. When the V(V) electrolyte with the same concentration as that of the unbalanced electrolyte is added to the unbalanced electrolyte, V(V) ions gradually oxidize V(III) ions to V(IV) ions, and the color of the electrolyte changes significantly. By extracting the RGB information of the electrolyte image, it is found that the B channel value presents the highest sensitivity to the V(IV) ion content. Thus, the relationship between them is fitted, and the R 2 of the fitted curve reaches 0.9978. Furthermore, the image analysis-based method is applied to predict the V(V) electrolyte volumes needed to repair the unbalanced electrolytes. Results show that the deviation of the B channel values between the recovered and standard V(IV) electrolytes is within 5%, demonstrating the effectiveness of the proposed repair strategy and image analysis-based method, which show great promise for practical VRFB applications.