Energy-Saving Synthesis of Vanadium Electrolyte by Zinc Reduction for Redox Flow Batteries

This study examines the possibility of producing vanadium electrolyte at low temperature by reducing V5+ compounds with metallic zinc in sulfuric acid solution. In contrast to conventional electrochemical or high-temperature synthesis routes, the proposed method does not require heating, current flow, or gas supply. Its novelty lies in demonstrating, for the first time, a complete transformation of vanadium from V5+ to V2+ under ambient conditions, realized in a simple and potentially scalable one-stage chemical scheme directly in sulfuric acid medium, fully compatible with vanadium redox flow battery practice. Two models were developed to simulate the reduction process: a simplified stoichiometric model and a time-dependent kinetic model. Both confirm the theoretical possibility of achieving complete conversion from V5+ to V2+ in < 30 min. The kinetic model provides a more realistic prediction of intermediate valence state behavior and electrochemical potential. The evolution of Gibbs free energy was also calculated throughout the process. In both models, ΔG remains negative, confirming the spontaneous nature of zinc-mediated vanadium reduction. In addition, the energy input required for several known electrolyte production methods was estimated and compared. The zinc-based method demonstrates the lowest energy demand, requiring only mechanical stirring at room temperature. Electrolysis and thermal methods show significantly higher energy consumption due to electrical current or high-temperature operation. These results confirm the feasibility and energy efficiency of zinc-assisted vanadium reduction in solution. The process does not rely on complex equipment and may be suitable for decentralized or batch-scale electrolyte production. The study provides a theoretical basis for further experimental validation and application in vanadium redox systems.