氢溴液流电池高电密充放电过程的多相多组分传输现象

Concerning the complicated phenomena of the multiphase, multicomponent transport in hydrogen-bromine redox flow batteries during the process of charging and discharging at high current densities, we, with the help of both experimental and numerical approaches, plan to investigate the following issues in this proposal: (1) The impacts of current direction and electrode wettability over the multiphase water distribution and the equilibrium between different water phases in the negative electrode (NE). (2) The transport of protons, bromine and different kinds of bromides, e.g. tribromide, pentabromide, etc. in the positive electrode (PE) and the equilibrium among them. (3) The transport of bromine and hydrobromide in the solide electrolyte and its impact on bromine crossover and water balance.(4) The parasitic reactions induced by local starvation of reactants and the corresponding electrode corrosion in both the NE and the PE at either potentiostatic or galvanostatic operations...The aims and significances of this proposal lie in the following aspects: (1) Gain a thorough understanding about the underlying mechanisms of non-equilibrium water transport during hydrogen evolution and oxidation in the porous hydrogen electrode, so as to enhance the charging/discharging efficiency and the capability of rapid switch between the charging and discharging mode in the NE. (2) Elaborate the coupled phenomena among the equilibrium of ions, electro-osmotic drag and diffusion of various molecules and ions in the positive electrolyte, thus laying theoretical foundations for solution optimization, for the optimization of charging and discharging depth, and for the development of numerical models. (3) Obtain knowledge pertaining to the content of dissolved water and bromide ions in the proton exchange membrane immersed in the liquid electrolyte solution at various state of charge, thus reduce bromine crossover and the ionic resistance of the membrane(4)?Explore the rates and threshold conditions of the parasitic reactions induced by reactant starvations in the the porous electrode, and provide strategies of fault diagnosis in order to enhance the durability and safety of the cell.

针对氢溴液流电池高电密充放电过程的多相多组分传输现象，运用实验与模拟相结合的方法研究如下内容：（1）电流方向与电极浸润特性等参数对高电密氢电极内多相水分布与平衡的影响。（2）正极氢离子、多种溴离子和溴分子的多组分平衡与传输问题。（3）溴与氢溴酸在固态电解质内的传输及其对溴穿透和水平衡的影响（4）恒流及恒压条件下，局部反应物缺乏导致的寄生反应以及正负极腐蚀现象。..上述研究内容的主要目的和意义表现在：（1）掌握多孔氢电极析氢与氢氧化反应过程非稳态水传输的规律，提高负极的充放电效率以及充放电切换能力。（2）阐明正极液中离子平衡、电渗与扩散的耦合关系，为溶液选配、充放电深度设计及建模奠定理论基础。（3）掌握质子交换膜处于不同充放电深度的电解液中溶解水及离子含量，降低溴穿透与膜电阻。（4）明确局部反应物不足时各类寄生反应发生的阈值条件与速率，获得电池运行异常的诊断策略，从而提高电池的寿命与安全性。

在大规模电能储存与转化过程中，液流电池凭借其高效率、长寿命、低成本及布置灵活的特点成为最具发展潜力的技术。在液流电池的多相多组分电解质中，反应物的质量传输、电荷传递以及电化学反应之间的耦合效应异常复杂，深入理解其中的规律是电池设计的关键和当前的研究热点。本课题围绕氢溴液流电池（HBFB）和钒液流电池内具有共性的反应物分子和离子传输及离子电流传导问题展开，着重研究了反应物输运、穿透损耗、泵功损失以及旁路电流损耗等影响电池效率的相关科学和技术问题。下面将课题取得的重要成果汇总如下：.1).我们建立了考虑电解液体相浓度与电极表面浓度差异的HBFB模型。在此基础上将电压损失分解成动力活化、欧姆和传质三部分损失并进行对比研究后发现：平衡活化损失和欧姆损失存在一个最优厚度；而厚电极有助于降低传质损失。另一个有趣的发现是: HBFB在放电过程中电压下降相当平缓，这主要是因为产物氢离子和溴离子的增加提高了离子导电率。.2).依靠对称电池实验，探索了电解液流速对电极内传质能力的影响。研究发现：流速低于5 mm/s时传质损失非常显著；当流速高于10 mm/s时，流速的影响明显减弱；5 至10 mm/s的液流速是推荐的优化区间。针对大型薄片电极流场引入的需求，我们还提出了设计过程中平衡压降、流速、均匀性及紧凑型的基本原则。.3).我们发现在正负极氢离子浓度不同的条件下，即使电池处于开路状态电场作用依然存在，从而导致阳离子从氢离子浓度低的一侧迁移到氢离子浓度高的一侧。此发现提示我们在测量膜中离子穿透特性时保持渗析池两侧氢离子浓度一致性对测量精度的重要影响。.4).基于相似电路模型和流动网络模型， 我们研究了多堆液流电池中涉及旁路电流、泵功损失和紧凑性的平衡问题。首次提出了利用粗长管路同时降低旁路电流损失与泵功损失的设计原则， 并研究了系统效率与紧凑性的平衡关系。.5).我们在碳毡电极内两相流动的实验研究中发现：几乎可以忽略的微量气相析出会在碳毡内部积聚并达到明显的含气率水平，并导致非常显著的液相渗透率的下降。对多孔电极内存在析气的大型液流电池堆而言，这一发现有助于寻求最优的设计与运行策略从而保证电解液配送的均匀性和效率。.6).多孔电极的压缩率及与之密切相关的渗透率在平衡电池的欧姆电阻和流动阻力方面具有重要影响。基于碳毡测试的思路与实验，我们申请了发明专利：“压缩率可调型多孔介质平面渗透率