传质对全钒液流电池性能的影响

The vanadium redox flow battery is the key device to store electrical energy. It can be widely applied in the fields such as solar energy, wind energy, power grid peak shaving, automobile power system, and so on.The bottleneck problems blocking its large-scale applications are low current density, electrolyte imbalance and the decrease of electric capacity. These bottleneck problems will be solved by analyzing the mass transfer in the vanadium redox flow battery. In this project,the simulatins of the mass transfer in the flow field of electrode, in graphite felt of the electrode and in the proton exchange membrane, and electrochemical reaction in the electrode are carried respectively by the methodes of macro-simulation, pore-scale simulation and micro-simulation.the results gotten by the experiments of the mass transfer in the proton exchange membrane, of electrode characteristics, of current density distribution, of AC impendance, and SEM images of the electrode and the proton exchange membrane are used to verify these simulation data; To reveal the influence rule of the mass transfer, the simulation and experimental results are used to analyze the effects of the flow field structure, graphite felt, proton exchange membrane, cell temperature, concentration of the electrolyte, electrical field intensity, and flux of electrolyte on cell performance,the balance of the electrolyte in electrode, the stability of electric capacity and the cell lifetime. these research results are used to lay the foundation of obtaining a high characteristics, high reliability and long lifetime vanadium redox flow battery and breaking its bottleneck problems of application.

全钒液流电池是大规模蓄能的主要装置，能被广泛应用在太阳能蓄能、风能蓄能、电网调峰、汽车动力等领域。电流密度底、电解液失衡和容量降低是全钒液流电池应用中的主要瓶颈。对全钒液流电池进行传质分析，可以找到解决上述问题的方法。本项目主要通过宏观、介观和微观方法分别模拟全钒液流电池电极流场传质、电极石墨毡传质、电极电化学反应和质子交换膜传质等；通过质子交换膜传质实验、质子交换膜和石墨毡结构观测实验、全钒液流电池电极特性实验、全钒液流电池电流密度和交流阻抗分布实验，来验证全钒液流电池电极、质子交换膜和电极电化学反应的模拟数据，分析电池流场、石墨毡、质子交换膜、电池温度、电解液浓度、电池电场、电解液流量等结构和操作参数对全钒液流电池性能、正负极电解液平衡性、电池容量保持性、电池寿命等应用要素的影响，揭示全钒液流电池中的传质规律，为获得高性能、高可靠性、长寿命的全钒液流电池及突破其推广使用瓶颈奠定基础。

全钒液流电池是大规模蓄能的主要装置，能被广泛应用在太阳能蓄能、风能蓄能、电网调峰、汽车动力等领域。电流密度低、电解液失衡和容量降低是全钒液流电池应用中的主要瓶颈。本项目通过宏观、介观和微观方法分析全钒液流电池电极流场传质、电极石墨毡传质、电极电化学反应和质子交换膜传质等；通过质子交换膜和石墨毡结构观测试验、全钒液流电池电极特性试验和交流阻抗分布试验，来验证电极传质、质子交换膜传质和电极电化学反应的模拟数据，分析石墨毡、质子交换膜、电池温度、电解液浓度、电解液流量等参数对全钒液流电池性能、电解液平衡性、电池寿命等应用要素的影响。研究结果发现：全钒液流电池主要阻抗因素包括一个欧姆阻抗，二个法拉第阻抗，二个容抗，正极法拉第阻抗大约为负极法拉第阻抗的3倍；电解液浓度增大会使欧姆阻抗和法拉第阻抗增大；电池装配压缩石墨毡到60%时，全钒液流电池性能最佳；电池处于过充时，电极和流场板会出现腐蚀，对反应物和生成物的传递产生阻碍；石墨毡电极经过MWCNTs和Hydroxyl MWCNTs修饰的全钒液流电池的电容量提高了15.3%和30.6%；装配预紧力和流场的存在使石墨毡内原本均匀孔隙率变得不再均匀，流脊下石墨毡内的孔隙率小于流道下石墨毡内的孔隙率，并导致反应物、电流密度和电势分布发生变化；电极中体积大和带电荷多的颗粒会降低该颗粒的扩散系数；质子交换膜内由水分搭建了水合质子的传递通道，温度和聚合物内孔隙率对水分和水合质子的传递有显著影响；在石墨毡电极中，羟基是电化学反应的催化剂，羟基首先吸附在石墨毡碳表面，钒离子通过羟基获得或转移电子，从而改变钒离子的价态。研究获得了全钒液流电池的最优操作参数、石墨毡的结构参数和装配参数，发现了全钒液流电池的阻抗特性、电极传质规律和电极电化学反应机理，突破了该电池推广使用中的一些瓶颈问题，为获得高性能、高可靠性、长寿命的全钒液流电池奠定了基础。