Study of the production of vanadium electrolytes from ammonium metavanadate

This work presents a technology for producing vanadium electrolytes with average oxida-tion states of V²·³⁺ and V⁴·⁵⁺ for application in vanadium redox flow batteries (VRFB). Am-monium metavanadate (NH₄VO₃), a comparatively low-cost raw material, was used as a precursor and subjected to calcination to obtain a mixture of vanadium oxides (V₂O₄ and V₂O₅), which are readily soluble in sulfuric acid. The conditions of calcination, chemical reduction with oxalic acid, and electrochemical reduction on a titanium cathode with a proton-conducting membrane were investigated. Optimal calcination parameters (5 h at 500 °C) were established, ensuring high solubility of the products. The electrochemical reduction method made it possible to obtain electrolytes with the target oxidation state at current densities of 1000–2200 A/m² and VO₂ concentrations up to 104 g/L. Cyclic volt-ammetry confirmed the quasi-reversible nature of the processes for the V³⁺/V²⁺ and V⁴⁺/V⁵⁺ redox couples, indicating high electrochemical activity of the electrolyte. The proposed technology reduces the production cost of electrolytes by using an accessible raw material and minimizing the consumption of reductants, making it promising for industrial ap-plication in VRFB-based energy storage systems.