Vanadium Electrolyte Prepared by Clean Crystallization Purification and Chemical Reduction of Crude V2o5 for All-Vanadium Redox Flow Battery

Abstract

Vanadium electrolyte is the most crucial component for all-vanadium redox flow battery (VRFB). High cost and serious process pollution for the production of vanadium electrolyte are the restrictive problems for large-scale application of VRFB. Herein, a novel and clean route for the preparation of vanadium electrolyte by crystallization purification and chemical reduction of crude V2O5 was proposed. Crude V2O5 was dissolved into NaOH solution and existed in the form of Na3VO4. The solubility of Na3VO4 in NaOH solution decreased obviously with the decrease of temperature. It was feasible to purify crude V2O5 by alkaline leaching and cooling crystallization. The effects of NaOH concentration, stirring speed, initial crystallization temperature and cooling rate on crystallization ratio of Na3VO4 were systematically studied. The majority of Al, Cr, Fe, Ca and Mg were removed by cooling crystallization. Na3VO4 crystals with a high purity of 99.9% were obtained. Na3VO4 crystals were further reduced and hydrolyzed to obtain VO(OH)2. Initial V concentration, reduction temperature, pH of reduction reaction, molar ratio of H2C2O4 to V and pH for hydrolysis were optimized. Self-made vanadium electrolyte exhibited good charge-discharge properties. Particularly, the cost of novel route was only 45.9% of that by traditional route, and no ammonia nitrogen-based wastewater and waste gas were discharged. This work provides a low-cost and green route to prepare vanadium electrolyte, which is beneficial to promote large-scale application of VRFB.

Keywords: Crude V2O5, crystallization purification, Na3VO4, vanadium electrolyte