Mn2+浓度对钒液流电池正极液的电化学性能影响

电解液中金属离子会影响钒液流电池的电化学性能。本文采用循环伏安法和电化学阻抗谱研究了正极液中Mn2+浓度对V髨/V(Ⅳ)电对的氧化还原过程影响规律,发现Mn2+在正极液中没有发生副反应,但严重影响V髨/V(Ⅳ)的反应活性、电极反应可逆性、离子扩散与电荷转移反应等电化学性能。循环伏安测试结果表明Mn2+浓度为0.04-0.13 g.L-1时,V髨/V(Ⅳ)电对电极反应可逆性和反应活性较高,钒离子扩散系数由参照溶液中的8.89×10-7-1.098×10-6增大至1.302×10-6-1.800×10-6 cm2.s-1,提高了-60%;电化学阻抗测试结果表明Mn2+浓度为0-0.04 g.L-1时,V髨/V(Ⅳ)电对电极反应阻抗和界面阻抗均较参照溶液中的增加不明显,但当Mn2+浓度增至0.07 g.L-1时,上述阻抗值较参照溶液增大了25%-28%。基于二者结果,Mn2+对电极反应有不同程度的负面影响,但是适当的Mn2+浓度有利于钒离子的扩散。

Influence of Mn2+ Concentration on the Electrochemical Behavior of the Anolyte for Vanadium Redox Flow Batteries

Metal ions in the electrolyte will affect the electrochemical performance of vanadium redox flow batteries(VRBs).The influence of Mn2+ concentration in the anolyte on the redox process of V(Ⅴ)/V(Ⅳ) couple has been investigated by cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS).It is found that Mn2+ doesn′t cause a side reaction,but greatly affects the electrochemical performance of V(Ⅴ)/V(Ⅳ)redox reaction,including reaction activity,reversibility of electrode reaction,vanadium ion diffusion,and charge transfer reaction.The results from CV show that the reversibility and the reaction activity of V(Ⅴ)/V(Ⅳ) couple can be improved as the Mn2+ concentration ranges from 0.04 to 0.13 g·L-1.The vanadium ion diffusion coefficient increases from 8.89×10-7-1.098×10-6 in the reference anolyte to 1.302×10-6-1.800×10-6 cm2·s-1,an increase of -60%.EIS investigation indicates that the electrode reaction resistance and interfacial resistance of V(Ⅴ)/V(Ⅳ) couple have a slight increase when the Mn2+ concentration is no more than 0.04 g·L-1.When the Mn2+ concentration reaches 0.07 g·L-1,the values of these resistances are 25%-28% higher than those in the reference anolyte.Considering the results from CV and EIS,Mn2+ has different adverse effects on the electrode reaction,but Mn2+ with proper concentration is beneficial to improve the diffusion of vanadium ions.