Polymer electrolyte membranes (PEM) for vanadium redox flow batteries

未来几年，德国可再生能源的使用量将增加。因此，用于这种波动能量的存储系统是非常重要的。储存能量的一种可能性是使用氧化还原液流电池（RFB），它很容易扩展。它们允许在液体可再充电电解质中存储电能。基于钒的系统（VRFB）是特别令人感兴趣的，因为钒离子存在于电化学电池中的膜的两侧。虽然钒离子在另一电解质半电池中的交叉将导致能量密度的降低，但不会发生由于污染而导致的系统的不可逆损坏。通常，聚合物电解质膜（PEM）用作VRFB中的隔板。特别重要的是Nafion，它是一种磺化的含氟聚合物。尽管全氟磺酸被用于许多商业应用中，但仍存在一些与全氟磺酸相关的缺点，因此开发具有上级性能的新型PEM材料非常重要。在跨学科项目中，新型PEM材料将在市售含氟聚合物薄膜和织物作为支架的基础上开发。氟聚合物的辐射诱导活化之后是接枝共聚以将允许磺化的官能团并入材料中。详细研究了辐射条件对自由基类型和浓度以及随后对聚合的影响。磺化后的质子交换膜的电化学特性和应用测试VRFBs进行。需要解决的重要方面是高导电性和防止交叉。实验结果构成了建立工艺、聚合物、结构和PEM性能之间相关性的基础。此外，实验还伴随着建模，例如，关于聚合过程的优化和通过膜的传质的描述。

The amount of energy from renewable sources will increase in Germany in the upcoming years. Thus, storage systems for this fluctuating energy are of high importance. One possibility to store energy is the use of redox-flow-batteries (RFB), which are easy to scale. They allow for storage of electric energy in a liquid rechargeable electrolyte. Vanadium based systems (VRFB) are particularly interesting, since vanadium ions are present on both sides of the membrane in the electrochemical cell. While cross-over of vanadium ions in the other electrolyte half-cell will lead to a lowering of the energy density irreversible damage of the system due to contamination does not occur. Frequently, polymer electrolyte membranes (PEM) are used as separator in VRFBs. Particularly important is Nafion, which is a sulfonated fluoropolymer. Despite the fact that Nafion is used in a number of commercial applications, there are some shortcomings associated with Nafion and the development of new PEM materials with superior properties is of high importance. Within the interdisciplinary project novel PEM materials will be developed on the basis of commercially available fluoropolymer films and fabrics serving as scaffold. The radiation-induced activation of the fluoropolymers is followed by a graft copolymerization to incorporate functional groups allowing for sulfonation into the material. The influence of the irradiation conditions on radical type and concentration and subsequently on the polymerization is studied in detail. After sulfonation the PEMs are electrochemically characterized and application tests in VRFBs are performed. Important aspects to be addressed are high conductivity and prevention of cross-over. The experimental results constitute the basis for establishing a correlation of process, polymer, structure and the PEM properties. Moreover, the experiments are accompanied by modelling, e.g., with respect to optimization of the polymerization process and description of mass transfer through the membrane.