Recovery of spent VOSO4 using an organic ligand for vanadium redox flow battery applications.

To recover the spent vanadium compound, Rhodamine-B-based Schiff's base ligand (L1) was synthesized via ultrasonication process and was evaluated with vanadyl sulfate (VOSO4), which has shown considerable selectivity towards V(IV). The change of the solution color from colorless to pink is attributed to L1 after the reaction with vanadium ion owing to the successful formation of the vanadium complex and the opening of the spirolactam ring in the L1 structure. In FT-IR spectra, the vanadyl peaks are co-existed with the L1 structure, which confirmed the complex formation of the L1 with vanadium. Similarly, the binding energy of V(IV) was identified at 516.2 eV for V2p3/2 in XPS spectra. The new strategy for VOSO4 recovery was established through solvent extraction and acid leaching. After recovery process, the absence of vanadium peak in the XPS confirmed the complete removal of V(IV) from the complex. The recovered VOSO4 solution used as an electrolyte in vanadium redox flow battery (VRFB) systems, where the unit cell performance is comparable with the conventional electrolyte solution. The advantage of study is reuse of VOSO4 as a resource for energy storage applications.