液流电池多孔电极孔内传质机理及其强化策略研究

Flow batteries have been regarded as one of the leading technologies for large-scale energy storage due to its high energy efficiency, large storage capacity, high safety as well as excellent reliability. Although attractive, issues associated with the unknown mechanism of microscopic mass transfer inside the porous electrode and the lack of effective mass transfer enhancement strategy substantially limit the performance of this type of battery. To address these issues, we propose to investigate the underlying mechanism of mass transport process inside the micron-scale pores of the porous electrode and its interaction with electrochemical reactions via both experimental and numerical approaches. Through the in-operando observation of flow distribution inside the porous electrode, the flow characteristics in typical flow battery electrodes will be revealed, and the synergistic matching issue between the electrode and the flow field will also be clarified. Then the symmetrical flow battery cell will be employed to elucidate the effects of porous structure, flow condition and electrolyte on the pore-level mass transfer coefficient and the corresponding quantification correlation will also be figured out, identifying the key factors that affect the mass transfer process inside the pores. By screening redox couples with unique fluorescence characteristics, the dynamic changes of the redox-active species concentration inside the pores will be captured by the home-designed in-operando observation device, revealing the effects of porous structure, local flow field and electrolyte composition on local concentration distribution characteristics of the regions near reaction interfaces. With the concentration distribution information obtained, the underlying pore-level mass transport mechanism then will be elucidated with the aid of the mass transfer coefficient correlation. At last, the transient three-dimensional theoretical model incorporating the pore-level mass transfer process will be constructed and verified to explore the coupling characteristics between the mass transfer process and the electrochemical reaction inside the pores and to optimize the flow field and the electrode designs for mass transfer enhancement as well. With the optimal designs obtained, it is envisioned that a substantial increase in power density and lifetime of the flow battery cell can be achieved.

液流电池因其能量效率高、储电容量大、安全可靠等特点，为规模储能的重要技术之一。但其多孔电极微观孔内传质机理不明、有效强化传质策略缺失等问题限制了该类电池的性能。针对这些问题，本项目拟通过实验和数值模拟等手段对电极孔内传质机理及其与电化学反应的耦合机制开展研究：通过多孔电极内流场在线观测实验，揭示典型电极内流动特性，明确电极与流场之间的协同匹配问题；探究孔结构、流动状况、电解液等对孔内传质系数的影响规律，获得相关量化关联式，进而分析影响孔内传质的关键因素；筛查得到荧光特征独特的活性电对，借助在线观测装置捕捉电极孔内物质浓度的动态变化，获得孔内反应界面区浓度分布特性随当地流场、孔结构、操作工况的演变规律，结合传质系数关联式阐明孔内传质机理；构建考虑孔内传质过程的液流电池理论模型，探究孔内流动-传质与电化学的耦合特性，并对流道和电极进行强化传质设计，实现液流电池功率密度和使用寿命的大幅提升。

电化学储能系统中，氧化还原液流电池具有优异的可拓展性、便于模块化制造、使用寿命长和安全性高等特点，被认为是一种具有广阔的发展前景的大规模储能技术。但是，当前液流电池传质机制尚不明确、有效强化传质策略缺失，限制了其性能进一步提升。不仅如此，多孔电极微观孔内流动-传质机理的研究较少，尤其是直接在线的可视化实验观测研究。针对这一现状，该项目从微观与宏观两种手段探究典型液流电池多孔电极在不同操作参数和装配参数下的传质特性。宏观上，通过构建对称电池对多孔电极孔内传质系数进行电化学法测定实验，而微观上搭建多孔电极孔内电解液浓度分布的在线观测平台，利用蒽醌类物质独特的荧光特性原位捕捉浓度分布特性，为探索多孔电极孔内传质特性提供新的思路。具体来说，首先以液流电池典型的石墨毡电极为研究对象，探究了压缩比、孔隙率以及电极厚度等参数对传质过程的影响规律，再比较了石墨毡电极与碳布碳纸孔内电解液浓度分布规律，探究传质死区产生的原因。基于以上认识，对多孔电极进行了强化传质设计，通过配位反应在碳纤维表面形成MOFs，接着在MOFs诱导下形成竖直结构的碳纳米阵列，同时引入对钒离子氧化还原反应具有高催化活性的铋纳米球，最终制备出了强化全钒液流电池传输和反应的铋纳米点嵌于立式碳纳米阵列复合电极，将电池性能提升至200mA/cm2下能量效率可达到85%以上。此外，在能源与传热传质领域发表SCI论文8篇，包括Advanced Functional Materials、Small、Journal of Power Sources、ACS Appl. Mater. Interfaces、International Journal of Heat and Mass Transfer以及Energy 等。其中，还申请发明专利两项。