The goal of this interdisciplinary project was to develop new Proton Exchange Membrane (PEM) materials for Vanadium-Flow-Batteries (VFB). These materials were based on commercially available fluoropolymer films as a framework material. The activation of the framework materials was achieved through electron irradiation, followed by graft copolymerization to introduce functional groups that are either sulfonatable or already proton-conductive. To evaluate the new materials compared to the current state of the art, both physical and electrochemical investigations were conducted and assessed. Additionally, a comprehensive understanding of the graft copolymerization process was developed using these experimental insights, forming the basis for the systematic development of an innovative reactor design to enhance reproducibility in PEM production.

While VFBs are already commercially available, the membrane remains a critical and cost-intensive component, requiring a more comprehensive understanding of Vanadium crossover processes for optimization. To address this, stationary and dynamic experiments were conducted, varying current density, state of charge, electrolyte concentration, and electrolyte management concepts to capture Vanadium transport within the membrane in situ. Based on these experimental results, it was possible to develop a membrane transport model to simulate the dynamics of Vanadium crossover and associated self-discharge reactions, enabling the evaluation of diffusion coefficients and dynamic material transport processes.

In summary, the study indicates that graft copolymerized membranes for VFBs could be a promising alternative to the current state of the art. This is due to the reduction in specific sheet resistance and Vanadium crossover, leading to a decrease in battery capacity loss. Furthermore, the study highlights the importance of dynamic material transport processes and self-discharge phenomena within the membrane.