Abstract:

To address the issues of lengthy preparation process and difficult removal of chemical residues in traditional chemical reduction-electrochemical reduction methods for preparing 3.5-valent vanadium electrolyte, this study proposes an innovative process involving NH₃ gas-phase reduction of NH₄VO₃, (NH₄)₂V₆O₁₆ and V₂O₅ precursors to directly obtain 3.5-valent vanadium oxides, followed by dissolution to prepare 3.5-valent vanadium electrolyte. Both thermodynamic calculations and experimental results demonstrate that the NH₃ reduction of NH₄VO₃, (NH₄)₂V₆O₁₆ and V₂O₅ follows a stepwise reduction mechanism: V⁵⁺V₆O₁₃VO₂V₄O₇V₂O₃. Enhanced vanadium reduction was achieved by increasing reaction temperature, NH₃ flow rate, and prolonging reaction duration. Optimal conditions were established as: 50 min reaction time, 100 ml/min NH₃ flow rate, and 480℃ for NH₄VO₃ reduction, 520℃ for (NH₄)₂V₆O₁₆ reduction, and 490℃ for V₂O₅ reduction. These conditions yielded electrolytes with vanadium concentrations exceeding 1.75 mol/L and valence states of 3.5±0.1. Notably, NH₄VO₃ and (NH₄)₂V₆O₁₆ precursors achieved vanadium concentrations above 1.90 mol/L. Analysis of the performance of the electrolyte obtained after the reduction of the three raw materials showed that the conductivity of ammonium metavanadate as the raw material was the best (ionic conductivity 19.17 S/m), which was 49.4% and 74.0% higher than that of vanadium pentoxide (12.83 S/m) and ammonium polyvanadate (11.02 S/m), respectively. This novel process eliminates organic/chemical reductant residues in electrolyte preparation, providing technical support for short process development of vanadium redox flow battery electrolyte production technologies.

Key words: vanadium electrolyte, ammonia reduction, NH₄VO₃, vanadium redox flow battery, (NH₄)₂V₆O₁₆, solubility, thermodynamic property

摘要：

针对3.5价钒电解液传统化学还原-电化学还原制备工艺流程长、化学残留难脱除等问题，提出一种氨气气相还原偏钒酸铵、多钒酸铵及五氧化二钒等原料一步获得3.5价钒氧化物-钒氧化物直接酸溶制备3.5价钒电解液的新工艺。热力学计算与实验结果均表明，氨气还原偏钒酸铵、多钒酸铵及五氧化二钒均遵循V⁵⁺ V₆O₁₃VO₂V₄O₇V₂O₃逐级还原原则，提高反应温度、氨气流量及延长反应时间均能促进五价钒的还原，在反应时间50 min、氨气流量100 ml/min条件下，在反应温度480℃、520℃和490℃分别还原偏钒酸铵、多钒酸铵和五氧化二钒，均可获得钒浓度1.75 mol/L以上、价态3.5±0.1的钒电解液，以偏钒酸铵和多钒酸铵为原料时电解液中钒浓度可达1.90 mol/L以上；对三种原料还原后获得的电解液性能分析表明，以偏钒酸铵为原料导电性最优（离子电导率19.17 S/m），分别较五氧化二钒（12.83 S/m）和多钒酸铵（11.02 S/m）体系提升了49.4%和74.0%。本论文提出的新工艺可避免3.5价钒电解液制备过程有机/化学还原剂残留，为全钒液流电池电解液制备技术的短流程发展提供了技术支撑。

关键词: 钒电解液, 氨气还原, 偏钒酸铵, 全钒液流电池, 多钒酸铵, 溶解度, 热力学性质